is the 70-200 2.8 IS suitable for indoor lowlight shoots?

For sure the f/2.8 will help you in low light condition, like indoor live music. Not like the 50/1.4 but you had not been disappointed. However, 85/1.2 or 135L do a better job in this case, specially in scenes as live music, theater and dance (stage).

On the other hand IS will help you in shooting without a tripod, specially when shooting at more tele angles, like 200mm. For this reason, I believe IS will not help you too much, because is difficult to carry a tripod in the stage or between the audience (at least in live music concerts).

thanks for all the responses guys/gals, they've been very useful.

the movement blur seems like it may cause some problems as hip-hop performances tend to be very energetic with lots of gesticulation so chances are the arms etc would always end up blurred although for the types of pictures i'd be taking from the back of the crowd i think that may be acceptable anyways. its the stageside close ups where blur is less desirable.

i've had a couple of ideas on how i could go about it.

i think i'll probably end up going for something like either

ef 35 f1.4
ef 50 f1.4
ef 85 f1.8
and maybe add the 135 f2.8 later on.

or

sigma 30 f1.4
ef 50 f1.4
ef 70-200l f2.8 IS
and maybe add the 85 f1.8 later on.

one thing i didnt ask about is the focusing speed of the 70-200l in low light. is it prone to hunting?