Do games optimize for multiple CPU's? I don't think the second CPU is going to help your gaming scores, only the 1st CPU. and then single core performance is going to matter most. Some of those older Xeons may have lots of cores/threads, but have pretty low clocks, so single core performance isn't very good.
I just checked, you're already looking at a lot more cores/threads than games can reasonably make use of, with just one of those CPU's, and the base and boost clocks aren't very high compared to a newer CPU, so you're going to bottleneck even a modest video card. I think you're just going to be wasting a lot of electricity for no real performance gain, trying to game with this system.