I just want to encourage you on a few things. I was once in a Christian book store with my kids and looked at BJU 8th grade LA. It was covering the exact same thing that my 5th grade daughter was doing in R&S 4. I mean exactly no more in depth at all. I was worried that perhaps we needed to "catch up". No longer do I even think about that. 
Also Cathy Duffy says that R&S 10th is very complete and they would be done with Grammar for high school at that level. So that would make it two years ahead at some point in the game. Here is the chart from R&S English. This is a non official site I would look at the teacher manula sample and by seeing what is covered in the year and looking at the student samples I was very accurately able to place my four into the right levels. Just throw that grade thing out though.
http://www.rodandstaffbooks.com/list/Bu ... sh_Series/Also with Singapore that stuff is crazy magic math.
We love it! It is real thinking math but I want you to know that my kids that were from ps and did fine with R&S math really struggled with Singapore from ps. My kids that have never been in ps breeze through it. So it takes a little time for kids sometimes to transition into it and they will "catch up" eventually. So I absolutely would not worry about levels when they get the hang of it they will move right back to their level. It's just a little training time of their brain is all that is needed. I hope I even answered your question. Welcome to HOD you are going to love it!
