New Sigma 50-150 f2.8 OS for indoor volleyball

I have been taking photos of indoor volleyball in poorly lit gyms and fast action. I have a D7000 and currently have a Tamron 25-75 f2.8 and a Sigma 70-200 non-OS f2.8. I find that I like the 70-200 - focuses faster and better reach but often I don't have enough room to back up and shoot mainly from the side of the court - can't get wide enough. I usually find myself with the 25-75 - which focuses a little slow in the low light and is too short for many of the photos. Most are shot between 40mm and 75mm - with 60-80% at 75mm. I was thinking about selling the 70-200 and getting the new 50-150. Anyone use this lens for indoor volleyball on a dx camera? How is the focus speEd in low light and will I miss the extra 50mm of reach on the 70-200 in some venues?

I have tried primes and just don't have enough room to move.

What would be your ideal set up (with only 1 body) for this usage? I usually am between 3200 ISO and 6400 ISO at F2.8 and SS at 1/800 to 1/1000.

Here is a link to lots of photos from this weekend - includes a some good ones and quite a few others so that I had at least a few of each girl covered. http://www.dlevinephotography.com/setpoint010513

Any feedback is appreciated.