As you have found out, the ST-E2 can be iffy.

On the one hand, I've used them to trigger strobes which were down a hall and around a corner.

But on the other hand, I've used them outside and couldn't trigger strobes which were only 20' away and to my 10-o'clock and 2-o'clock.

In an open gym, you might be lucky to get 20'~25' if your strobes have a direct line-of-sight to the transmitter (meaning that you have to have the body of the strobes facing directly at you while the strobe head can be directed elsewhere).

I believe that the 580EXII has the same transmitter that is in the ST-E2 so there probably won't be any difference in performance. I'd use the ST-E2 so you don't flash the people directly.