Thanks guys. That's pretty much been my approach (with one exception). I try to find the best presenting, well-centered copy I can get in 8.5 or above.
When I first started collecting CGC FFs, I was lucky enough to pick up the FF 149 CGC 8.5 and FF 148 CGC 8.5 as my first purchases for a really good price. They both present very well, and I thought "if this is what 8.5s look like, I don't need any higher grade." These however have been the exception--other 8.5s haven't looked quite as good, though. To be quite honest, several of the 9.4s I have don't look as good as these two 8.5s. I'm not sure what brought the FF 148 down, but I called for the graders' notes (when they were still free) on the FF 149 (light spine stress, fading at spine)--I think the fading at the spine is what really caused the lower grade. The fading doesn't look that excessive to me, and I'm not sure it's not just a printing defect.
So, the FF 149 has been my only exception to just sticking with a nice presenting, well-centered copy and not worrying too much about the grade. FF 149 was the first comic I purchased off the rack at my local 7-11 as a kid, so it holds a special place in my memories. I came across this nice CGC 9.6 copy of it (but I've held onto the CGC 8.5 copy as well). Sadly, I probably could have gotten two other books I need for my run for what I paid for the FF 149 CGC 9.6.
Here's what the 8.5 and 9.6 look like.