Thanks for all the suggestions so far. Just wanted to clarify a few things...
1) My wide angle lens is mostly my Canon 16-35mm f/2.8. Usually I bring my 24-105mm f/4 to school because 105 (or 168 with 1.6x) is suitably long enough to get candid shots of people on stage, and 24 (or 38 with 1.6x) has been ok so far when group shots were needed, as long as I stood a few steps back. In my school hall, I'm used to settings such as 1/50-1/60 shutter speed, f/4, ISO 800. I also have a 24-70mm f/2.8 and a 70-200mm f/4 non IS.
2) If I'm not wrong, 500D and 5D Mk II both have between 3-4 fps? So if 500D is working well enough for me right now in terms of fps, I think that 5D Mk II would as well?
3) If my 70-200 is working all right for me now (at 116-320 with 1.6x), then wouldn't the closest be a 100-400 on a ff body?
4) My school events are held either in the hall, in the field, at external sports complexes or external concert hall. If it's in the hall, I'd use my 24-105 with settings as above, maybe with 16-35. In the field, or at external places (in bright sunlight), I'd use my 70-200, with faster shutter speed, lower aperture, lower ISO, to get smallest field of depth while not blurring out so that I can get those 1 or 2 sports guys involved in the action at that point of time.
Comparing 5D Mk II with 7D:
I think I could bring 24-70 + 70-200 for the hall events on 5D Mk II, but on 7D I'd stick to 16-35 + 24-105. I'd have enough length coverage on both bodies, just maybe a problem for blur on 5D Mk II, unless I raise the ISO (which I hear is less of a problem on this body.)
For sports, I'd have to get a 100-400 for a 5D Mk II to compare with 70-200 on 7D, but then the main difference would be fps here. But currently I don't really need the fps, since I have lots of time to carefully aim and shoot. I don't need to take shots in succession, just need to time them right. Usually in team sports like soccer, rugby, I'd have over 1 hour to slowly take my shots. In other sports like swimming or track, I'd have shorter time but less unexpected events. Bear in mind I only need 2 to 3 REALLY nice shots for the school magazine each time, not like 30 shots.
Just wanted to give a little bit more info on my usage and my thoughts. But thanks so far for all the suggestions! I haven't really looked at Sigma or Tamron lenses, but I think I might.