I have to ask, if you already have a 100-400 & 35-350, why consider the 28-300? You seem to have the super zoom range pretty well covered. Would you not be better off with a 24-105L f/4 together with your sharpy sharp 100-400? Then just leave the 35-350 for those times when you are not sure what the subject will be.
Just a thought as I'm not sure what you are trying to achieve?
Yes, Andy, I see the point you are making, actually I already have a 24-105L IS, and the reason for my post was I was interested to see if anyone had experience with both lenses ie 35-350v28-300.
I find since I got the 2 (24/105 and 100/400) I'm really not using the 35/350 except for rare occasions and as I've just got a 1Ds mk3, I suspect that whereas before I used the tele on the 40D and the wide zooms on my old 1Ds mk1, the autofocus may be such on the new camera that I'll want to use that with the tele lenses and the 24/105 on the 40D, although obviously losing a bit of w/angle.
I need to do some tests on the 2 autofocus systems to see which is better, or indeed quicker, and as I only just got the new body, I haven't had a chance to do that yet.
Sorry if that sounds a bit tortuous, really was just doing a bit of fishing of other people's experience.
The 28/300 is a really expensive bit of kit, though.
What I think I'd really like is a 400mm prime, but although everyone sings the praises of the 5.6, I can't see it being a huge improvement on my 100/400, so might have to save up pennies for a larger min aperture on, although I've heard rumors that the DO one is a bit soft. Oh dear, choices!!