626 mains, with 106 tails is about the limit. If you intend on smacking the aircraft around, I'd recommend synchronizing your tail rotor to the mains so they're never over each other. The 4.5 ratio works well for this. An even number of rotations with a half offset means the tail comes back to essentially the same position as each blade passes over it (symmetrical system, the .5 can be ignored). I tried 96 tails on a 4.5:1 ratio at 2100 for a while, and found that while it held fairly well, something like a quick tail down funnel or quick left-right piro reversals would get ugly.
You'll need to back the back-side of the tail case off to rotate the tail output gear. Also a good time to check the mesh and shimming back there. Bearings too if you have a minute.
