At f/1.8 indoors though my 550D has sometimes gone to ISO 6400 to maintain 1/500s. f/1.4 would at least help reduce noise.
Considered going full frame? I don't think you can get critical image quality from APS-C sensor, Nikon D7000 probably gets you closest (with the similarly sensor-ed sony and Pentax much the same). Even there ISO 3200 is a strong limit.
In those kinds of conditions a full frame camera might be needed, D700 has very good low light. Massive budget difference i know but sometimes you just have to accept limitations.
The f1.8 lens I'm using at the moment, has plenty of dof in the arena. So I'm not too worried about that.

, I've been looking at the images 100% crop.