Nat
I am one of those who tends to avoid the indoor gigs (good post, PossumCorner) so I can not really advise on specific lenses for best result.
However I HAVE shot indoors with my Sigma 70-200mm/2.8 and Tamron 28-75mm/2.8. I had to bump the ISO up still and do a fair amount of post processing though.
I wasn't expected to do movement shots so I wasn't under the same amount of "pressure" in that regard. I have done a few movement shots here and there (my choice, not a requirement), but again HIGH iso and a fair amount of post processing. Could not avoid it. Will see if I can find a sample.
With the venue you arent just at the mercy of the 3-mix lighting PossumCorner mentioned but the windows/doorways can also make for terrible "hot spots" in the background. Did you notice that PossumCorner?