Picking up a second body soon.

I know this question has to be the most common question on the forums. Which one should I get? So I have two cameras in question, First being the lovely 7d and the little brother the 50d. Since I will be doing alot of dance photography in very low light situations I am looking for something that works with with high ISO which I know the 7d is great with but how would the 50d perform in the 800+ ISO range? Currently I have a 30d and could use a body that is a little quicker and performs better in low light. So I was thinking if I don't need the 7d's video, would the 50d suit me perfectly meaning saving some cash and getting another lens along with my 50-150 f2.8 to compliment my shooting style?

Should I rule out the 60d?

I don't think I put my thoughts together correctly haha. But I'll try simplify it... I'm looking to upgrade from my 30d and use my 30d as my second body. Heres what I need in the body...

Good low light performance (better then the 30d at 800+ ISO)
Quicker FPS (I dont need much more but a little would be nice)

I know I can get this out of the 7d, but could I get the cheaper 50d and then a nice lens to compliment my 50-150 f2.8 at the same price as the 7d. I know you might say why not just keep the 30d but it's getting old and I don't want it to fail when I'm shooting a dance performance (500-1000 pictures).

So what do you guys think? 7d, or 50d with a nice medium range lens?