I only have a 5 foot frame, andI have used it to quilt near king size quilts. No, it is not ideal, and likely not "professional", but I get the job done. I work in quadrants. so very similar to what you describe, but I off center it a little more, just to avoid running into the sides of frame at all. quilt a quadrant, rotate, and do it again. I do not quilt the whole way down the side of the quilt because of the bulk and pull as described by MKC. most of the time, I can get the whole quilt done in just those 4 sections. but other times, I cant. this is what I do in those cases...hope it makes sense. I use those snap on quilt clips to position the quilt on the back bar instead of pinning it to the leader on that bar, tucking the extra material and such out of the way of the machine. then conitnue to float the top as normal. This allows me to target specific areas that I missed or couldn't get to. I doubt you would have to resort to this method, but it is an option.
If you do this or even if you are able to do it in the simpler way you describe, or if you just minimize your side overhang, I highly recommend basting it very very well before doing any of it.