The Well-Trained Mind recommends using FLL through V2 and then moving to R&S gr3. We started last year with R&S gr3 and LOVE IT! I will look into FLL for the littles when they are at a point they can use it. (I looked at it enough to know it's above my 3 and 4yo just yet.) I'll compare and contrast both of them at that time.
But, after v2 we'll definately be moving into R&S even with the little ones. Since gr3 is the only one I've used, I can't say, but I would imagine that it would be difficult to pick up R&S in 5th grade unless the child had gone through 3rd and 4th with it as well. Does that make sense? If you're going to switch to R&S for English at SOME point, I've seen it recommended in more than one arena that the time to do it is the 3rd grade.
I haven't looked at all at FLL beyond the first few lessons of the first book. With the book in front of you, and CBD or Amazon for TOC for future volumes, I'd compare what is taught with each and see how smooth of a transition it would be to do another year or two of FLL before switching. I do know that FLL only has 3 or 4 volumes, at least now, so you'll have to switch to something at some point.
And, I can't say enough about Rod & Staff. We LOVE the curriculum and will likely use it from now on, at least for English.