I have narrowed down to the following in my budget:
Canon 70-200 f2.8 VRII IS
Canon 70-200 f2.8 non IS
Sigma 120-300 f2.8
Tamron 70-200 f2.8
If you can afford the 70-200mm f/2.8L IS II, get it - it's really a no-compromise lens. Excellent for sports, fast AF, great IQ. The Sigma 120-300/2.8 OS is an interesting possibility, too…but as you say, the AF speed is likely to be an issue for you. The same will be true of the Tamron 70-200. The non-IS version of the Canon 70-200/2.8 is good…but the 70-200/2.8L IS II is likely the best telezoom available today. The only better choice than the 70-200/2.8L IS II would be the 300mm f/2.8L IS II - and that's way out of budget.
You can add a 1.4xIII to the 70-200 II, and the IQ will remain very good. AF will be slowed down, but I find the combo still quite fast, so it might work for you.My other lens choices for portraits/event - low light subjects are as follow:
Canon 24-70 f2.8 used
Canon 50 f.14
Tamron 24-70 f2.8
Sigma 85 f1.8
From that list, I'd be inclinced to go with the Tamron 24-70/2.8. IQ is almost up to the level of the Canon 24-70/2.8L II. The VC won't really help for events (at least, events with people moving).DXOMark has some nice scores (27) on the the Tamron 24-70 and while I can't claim to understand fully their testing it seems like a decent compromise. The score of 28 on the Tamron 70-200 f2.8 makes me think third party lens might be a way to work out this purchase. I did get rather confused over the issue of the 5d recognizing third party lenses.
Ignore DxOMark's Scores - they are actually based on 'performance in 150 lux illumination' (like a dimly lit warehouse), which is why the $100 50/1.8 scores higher than the $13,000 600/4 II. If you dig into the measurements, you can find useful info, but the top line Scores are worse than useless, IMO.
Exactly my thoughts. I have a near mint Nikon 200-400mm f/4 VR that I picked up for $2500 that would work well. I bought a used D300S and a cheap gimbal head just so I could play with it.
DXO rates it as a 12 with the D300S, and a 25 with a D800, so I am using the wrong body with it. That's a huge difference considering that the lens never changed. Its a good example of why the DXO score can badly mislead a person.