Tele-zoom for Canon?

So I am in the market for one more lens to fill out the first iteration of my SLR kit. So far I have:
Canon 40d
Sigma 18-50 f2.8 (i wish it was stabilized and USM, but the canon was 3x as much)
Canon efs 60mm Macro
Canon 28-135 Zoom (kit lens, variable aperture and kinda cheap feeling)

So I need something to cover the mid->telephoto range. I don't think I need anything too long, my last camera went out to the equivalent of 400mm, and I almost never used that length. I've narrowed the choice to three Canons, and was hoping for thoughts from the assembled wisdom:

EF 70-200 f4L IS (172mm x 76mm / 760g) -- oooh, look at that gray lens
EF 70-300 f/4.5-5.6 DO IS (99.9mm x 82.4mm 720g)-- lose 1/2-1 stop, gain 100mm and it's smaller. I like the idea of DO, it SEEMS so special, I just don't know how this lens plays in real life.
EF 70-300 f4-5.6 IS (142.8mm x 76.5mm 630g) -- cheaper than the other two, but less well built. Larger than the DO, but slightly faster. non USM(i mean it is usm, but not ring, so it's not as fast or quiet)

So I'm left with these tradeoffs:
F4L-- shortest and largest, highest quality glass and best motion (the other two change length in zooming)
DO -- compact, slowest of the three, some issues with zoom weight(hard to zoom in pointed down/hard to zoom out point ed up
70-300 -- cheapest, no ring USM

thoughts?
-a

 

I've shot with two of those three in the recent past - the 70-200mm f/4 and the 70-300 f/4-5.6.

The CA control of DO is interesting to me as well, and I've yet to test it out, but given how easy it is to filter moderate CA out in post-process, I'm not sure that I'd make a purchasing decision on that alone. Having not shot this lens, however, I can't offer much insight on it as a photographic tool.

Between the two that I'm familiar with, it's really no contest for me: the f/4 wins out for sharpness, construction, and handling. I tend to operate on the old adage that you buy camera bodies for a year but you buy glass for a lifetime, and if you can swing the extra cost of the 70-200mm f/4, I can't see a reason not to that way.

dr