Hi Chris.
Depending on the venue and available light, and of course which lens would you be using? I have taken some great shots using the 5D2 in AI hi-speed(wouldn't really call it hi-speed though!!), but your keeper rate won't be that fantastic because the frame rate being so slow, you jump a little too much between shots. Of course, if you're tracking, and anticipating, and are good at it, you can get some decent shots. The center point does work really well, too. There is a guy on DPreview forums, who swears his 5D2 center locks better than his 1D4 center point in low light....
My personal preference is the 1D4. I try to frame the way I see the shot, thus not having to crop too much. Having 45 points that, once again, as far as I'm concerned, lock all as good as the center point, lends to that task(framing). Plus, the auto-focus is blazing fast on the 4. Especially coupled with the new 70-200 2.8ll(rarely leaves either camera, by the way!!). With the 4 and 10 frames, you could burn shots, trying to get the perfect one....digital is sssoooooo nice!!
Both have great hi ISO, and with today's noise reduction software( I use Nik Dfine 2.0...but looking forward to LR 3 for comparison), I think you have more play in the 1D4 files(especially raw, the only way to shoot, BTW). The 1D4 files just have a LOOK to them, even at hi ISO, with a really good film grain feel.
I think you could survive with the 5D2 if that was you're budget...especially with a couple of fast primes. but the 1D4 would be my choice for that particular situation. Then again, not having used a 7D, that might work, too. I've just read that anything above 1600 or 3200 on the 7D, you really start to push your luck...
GreggF