I suppose it depends on the areas you wish to get to, and you're reason for wanting so much living space. We like mountains and mountain lakes, and there are those difficult to get to - impossible for a large Class A because the gravel roads have very tight turns, or other minor obstacles.
For us, anything over 30' would be too restrictive. Height is another consideration, if you're Into wooded areas...
Just consider where you plan to boondock and buy appropriately.