Canon 2X Teleconverter

I continue to be disappointed with the Canon 2X Teleconverter on the 70-200 f/2.8L lens.  Yeah, I got the shot, but it's not the clarity that I wanted. 

This was taken at ISO 1250, f/5.6, 400mm, 1/125th of a second.  Probably too slow considering it was 400mm.  But the light inside was just too weak.  I guess I could have gone to ISO 4000 to get the shutter speed up.

I guess I'm really only going to be able to use the teleconverter outside.