Ladies,
These are good questions and ones that we have spent quite a bit of time pondering ourselves, especially as our oldest son has now entered those final middle school years leading up to high school. What we have come to is that there are other ways to meet the science standards in middle school than by doing a barely down-sized version of high school science. At HOD, we are all about balance, and while it is certainly important to cover the necessary science concepts required for grades 6-7-8, there are more ways to do it than the textbook route.
With the upped requirements in science in high school, it is a sure thing that we will be spending plenty of time in that particular area during our kiddos' high school years. In our opinion that is fine for high school and suits the higher level of rigor expected for a high school student. However, in middle school, the level of rigor should be less and science should take a less than center stage approach. Yet, many of the programs we looked at do not allow that to happen.
Apologia's courses can take an hour and a half (and more often even 2 hours) daily, depending on how detailed the lab reports are done. This time allotment does not fit well within the balance among the subjects that we strive for at HOD, and it can also lead to early burnout over science for both parent and student. The size of the textbook alone is daunting! Rainbow science takes much less time (only 3 times a week) and has a slimmer textbook but requires a very expensive science kit and a 2 year commitment to cover its material. As a deciding factor for that program, we found the text to be pretty factual and not very living, presenting science as a body of facts with humor woven in. Its succinctness also seems to leave some concepts not explained in enough detail (making it tough for not very science-minded parents to struggle to explain).

Bob Jones and ABeka are not very homeschool friendly in their included experiments, making them tough to do well at home.
We have visited with many homeschool parents and read endless posts on other boards to see what the feeling is in the long-run with science. Most parents seem to feel that while high school science is very important in following an exact sequence and including labs where required, middle school is a time to develop a love of science when the requirements are much less stringent and there is still time to do so. Kiddos who are very science-minded will still be very science-minded in high school, and (in our opinion) not be held back by not using an expensive lab science or one with a textbook like an encyclopedia.
My older sister has 7 children who were all homeschooled from the time they were preschoolers. Her oldest 3 now attend public high school. Her oldest daughter did 2 years of Apologia in middle school with it taking her up to 2 hours daily. She thinks her high school courses have never been as rigorous as her Apologia middle school texts (and she is going into pharmacy this coming year at college). She did not enjoy her science until she got to public high school and never considered a science field before that due to the overwhelming feeling she had with Apologia in her middle school years. Her brother, who is now in high school as well, did 1 year of Apologia, and while math is his strong suit and he is headed into engineering, he too took forever to complete his Apologia assignments. The third child, a daughter, had only a few weeks of Apologia science in middle school, before heading into public school, and says that none of her middle school or her present high school science has even been as close to as difficult as her few weeks of Apologia (and she is a freshman now). Each of these kiddos is first, second, or third in their class of over 600 students, so I think their opinion that that type of science is "over-the-top" for middle school is one that I value.

Now you may be saying that more rigor is what you WANT and something you are looking for, but sometimes as homeschoolers in our quest to outdo the public school, we go over the top in the level of difficulty and rigor we require of our kids. Not feeling able to "do" the science at home also contributed heavily to my sister's choice to put her older kiddos in school. This is something that matters to me, as we desire to finish the call the Lord has made upon us to homeschool our kiddos. My sister's 4 younger ones are still at home being homeschooled.
At HOD, we will make sure to cover the science standards with our choice of texts and within our written work, however it will be done within a framework that looks at balance among all of the subjects. We will be covering the science standards by drawing out the study over 4 years, rather than doing it all in the final 2 years of middle school. In our desire to equip parents to homeschool for the long haul, we will be reasonable about what is required to equip our kiddo's for success in high school (and beyond) while balancing that which can be managed well at home.

We also desire for our kiddo's to have a different science experience than the textbook and lab science we endured in our public school days.
It's interesting to note that thinkers like Benjamin Franklin and Thomas Edison did not have much formal science, beyond plenty of time to read, ponder, and to try their own experiments. I ask you to think about how many students (once they enter "formal" science study through textbooks) do much of their own reading, pondering, or experimenting, or does it just become an assignment to be completed? Within our homeschool, we desire to encourage our kiddos to love science, to learn about science by getting to know the scientists through reading biographies, to see it as a way to show God's handiwork in all things, to test and try things, and to think deeply about why things work the way that they do. These goals for middle school can be accomplished with the resources we're listing above.
Now, if you have a very science-minded (and mathy) kiddo, or if you are very science-minded yourself, you may enjoy Apologia or Rainbow Science (or a different textbook science) for middle school very much. Through exhibiting at conventions we have had a chance to meet the authors of both of these curriculums and find them to be amazing gentlemen with a heart for the Lord and a passion for science. We just strive to provide something different in the way of middle school science instruction for those who may not desire to follow the more traditional path during those years.
You are always in the driver's seat as to your child's education, and we respect that with all our hearts! The programs I mentioned above (Apologia, Rainbow, BJU, and ABeka) are solid programs and are loved by many families. We will definitely be exploring these options for the high school science years! For middle school science, the deciding factor on what you use is on your family goals for science. As always, if your vision for science differs with any of our recommendations, you can easily use your own choice instead without affecting the rest of the HOD guide!
Blessings,
Carrie