The only thing that stops you with bison is the fact that its worthless until you are at 60% or less hp. You can still have it up when you are higher than 60%, but it does nothing.
I've honestly tried everything I can to keep my health at 30% when I level. Problem is, if I don't take VR, then I get killed a lot, and if I do, I don't go under 30% :(
I'm afraid that would put me with too much regeneration as well :(. I usually have full Prophet buffs (minus the 76+ ones), 78 SE buffs, and dances. I have been meaning to try it without VR, but just PoW. I haven't got around to it yet