- Will I be constrained to a max res of 3840 x 1024 due to the smaller monitors?
In Eyefinity, Yes. But you could try configuring SoftTH, but I think it's too much of an issue.
Make two profile: 1 Eyefinity for Gaming, and one That uses extended monitors for normal use.
Also a note, since in eyefinity the 1280x1024 will stretch, make sure to use the right FOV, so it's less noticeable. So when calculating the FOV, use 4480x1024 as your surround resolution, but when playing a game use 3840x1024.
- How do the ATI cards handle 3 different size screens in general?
Well in Extended Desktops, not so well in eyefinity (as you have to use the same resolution across all screens).
- Id really like to get up to 5760 x 1200, so I'm considering selling all 3 in favor of 3 Dell P2210H's which already have the displayport. Is it worth the hassle?
YES. It's really worth it. As it's better supported, Will look better, more screen real estate. More Resolution.