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.