Upload & Sell: On
Welcome Ben. I see you have a 7D now. Me too.
What sports were you thinking of shooting? If good natural light, the 70-200 f/4 is just fine. You'll need fairly high shutter speeds for sports, so you may not get a $500 benefit from the IS. The IS will only help with camera shake which is typically an issue at slow shutter speeds, and for sports you'll need higher speeds. Lately I've actually been turning off the IS on my 70-200 when shooting sports.
The bigger question might be whether 200mm is long enough. I think it's fine for Little League or softball with the shorter basepaths, or the smaller soccer fields. Kind of short for a lot of wildlife, unless it's outside your window (I'm serious about that - I have some great shots of birds through my window with a 70-200). The 7D will let you crop quite a bit, but that will only get you so far.
If you go with the non-IS 70-200 f/4 (which I think is a great choice for your first L), you could use that for a while and if it's not long enough, you could spend the savings (over the IS version) on a 70-300IS (about $600, not the L or DO versions) if you need longer.
I used a 28-135 for years as a mid-range, so I'd keep that. Same with the 50mm and the 18-55. I assume the other lens you have left over from the XTi is an 80-200 f/4.5-5.6 (not a 70-200). Not worth much, but you could definitely try sell that if you go for the 70-200L.