Upgrade from 75-300 IS to 70-300 DO IS?

I currently use and like my 75-300mm IS, but after looking into the 70-300mm DO IS with the better gen 3 IS and the faster AF speed I have been thinking of upgrading.

One of my many uses for my lens is sports, racing in particular...any one ever use the DO lens for this the 75-300 AF hunts slowly and for most action I have to turn off the IS. Would an upgrade to the DO IS cure my issues?

I'm very attracted to the smaller DO IS size vs. the 70-200L of the same price range.

I also find the 200mm of the L glass to be just a bit short sometimes for my needs as well.

Basically is it worth my time and effort to sell my 75-300 IS and upgrade to the DO IS for sports photography. I have other uses for my meager hobbist gear but I really only find my lens wanting when it comes to action.

I know the L is the sports norm but the IS L glass runs a bit more$$$ and the size is really huge. I can get my 75-300mm IS in a Tamrac daypack with gear as an airport carry-on with ease, I travel some. Not sure I'd do that as much with larger L glass.

Only if you would otherwise leave the camera at home, buy the 70-300 DO IS. If you want the best sports shots and don't care about size, buy the 'L' lens and add a teleconverter if you need the reach.

I love my 70-300 DO, the new gen IS is excellent, but it is not a 70-200 f2.8 'L' by any means.

Does size really matter?
At http://www.e-fotografija.com …publish/article​_306.shtml there is a comparison between the Tamron 28-300, the Canon 75-300 IS USM and the Canon 70-300 DO IS.
I own the Tamron 28-300, my wife has the Canon 75-300 IS, and the Canon 70-300 DO IS will arrive at my door at the end of the week.
I like to shoot motor sports, among other things, and get there by riding my bike. I therefore like the small, relatively light DO. If it weren't for the bike I would go with the 100-400 L IS for image quality and reach. I hope to have the 100-400 L someday too.
I guess the real question for you is: "Is the [COLOR=lime]DO worth the extra coins?"
I would only go to the [COLOR=lime]DO if the small size is more important than the image quality. It obviously was to me.

The size of the DO is very attractive, I've used both the 70-200L f4 and the f2.8 non-IS in the past. Both were excellent lenses, I'm just not sure I want to lug around the 70-200L f2.8 it would be my other choice vs. the DO.

It's usually a sunny day when I shoot, so I wonder if the newer gen 3 IS of the DO in mode 2 would help hand held and on a mono-pod? I currently must turn off my IS with my current lens. And from the stand point of AF speed, my drebel is likely the weak point, but I don't think the 75-300 IS helps much either

70-300 DO is a fine lens. Get the kenko 1.4 400 dg pro TC and youve got a real compact monster. (canon TC's wont work on this lens)

High Dante, I've seen some of your other DO IS posts.

Do you have much to rate the AF speed against? Does the lens hunt much say on the Drebel? Even in bright light my 75-300 needs time to adjust from close to far focus--seams like alot of time And do you use the IS on the lens much vs. hand held stills, still action is about all you can use the 75-300 IS for, nice at weddings but aweful at football and autoracing.

The Do is a pretty fast focusing lens.. I think it's right up there with the 100-400mm for AF speed..
But the 70-200mm's will be quicker.

It is very quick to focus. Remember it is a DO IS USM. USM being the key here. USM is great on this lens and for me I has yet to hunt. This is a quality lens that I think lives up to its price. I cant say how it would perform on a DReb, but I think you would be quite happy with it.

I'll have to keep this in mind, my 75-300 IS has been such a good friend dispite it's short comings but my new list of lenses includes the 70-300 DO IS, the 70-200L f4 now for the speed, and the 200L 2.8 simply from the prime speed stand point.

If I get the DO I have to sell my 75-300 to help fund the thing, but the others I can get without selling my old, somewhat slow friend.

It would be nice if the f4 70-200 came in optional black