Canon 70-200 f2.8 is ii vs f4 IS for the non-pro

It depends on just how low the light levels are and whether you can use flash. I have successfully used a 70-200 F4 IS with a 1.4X multiplier i.e. at F5.6 rather than F4 for indoor tennis using a 30D rather than a 7D, so it is possible. I was using a tripod but that was mainly to rest my arms because I was there all day.

With flash or stage lighting it will work OK for indoor performances. I have also used the 10-22, 17-55 and 100 F2.8 macro for indoor performances without flash. With flash and enough space the 70-200 seems to produce the best portraits of the lot.