Will the 28-135 be enough?

I'm about to purchase a 40D (I had decided on the Rebel XTI until I picked up the 40D). I can only afford to buy 1 lens initially and I had thought about the 50mm 1.4 since I'm going to be taking a lot of photos of my kids school programs in gymnasium lighting. But now I'm starting to wonder if maybe the kit lens would be better overall since I'll have more range to work with.

Will the 28-135 do ok in gym lighting with the IS or is it still going to be too slow?