I have the 24-70 f/2.8L and the 20 F/2.8. DO you also think the 16-35 f/2.8L is overkill?
What would you be shooting with the 16-35mm? Reporters like this lens because it's wide
and fast...but for less demanding shooting, landscapes for example, the 17-40mm F4 L, is probably a better option. Large apertures really aren't all that important with wide angle lenses anyway. Besides, the 17-40mm is a great bargain for an L quality lens.
Do you think I should take my money and upgrade my 70 - 200 f/2.8 non-IS to the IS version?
Tough question...but if you can sell the non-IS for a good price...I'd probably go for it.
When I bought my 70-200 F2.8 IS, I knew that if I went with one of the cheaper models, I would regret it sooner or later...and I'd always be wondering if I'm missing out. At least when you have the F2.8 IS, you know you have the best lens (not counting the primes, of course) and that peace of mind goes a long way.
Another issue is just how much quality to you actually
need. A photographer that makes their living with a telephoto might need the quality of a long prime...but most others would probably be happy with the 'lesser quality' from using TC and/or zoom lenses. For example, I've used a 70-200mm F2.8 lens with both a 1.4X
and a 2X TC attached. I've always recommended against this because of the quality loss...but it really wasn't all that bad, especially in the centre of the frame. (granted, I was using a crop body, a full frame might have much worse edges).