So what do you think? 1GB or 2GB model? I'm leaning to 1GB.
I don't think a 2GB 5850 would help you. Check out my review of the
5870 E6 card. I compared the 1GB and 2GB cards. The extra VRAM only game into play in specific games in specific circumstances. Considering you're not a graphics whole, and not running at 5760x1200, then I don't think you will use it at all.
Another quick question. My intent is to connect my TH2Go via DVI and also have an HDTV connected via HDMI to the 5850 for an extended desktop. I assume this will work with the card and ATI's CCC. Do you forsee any problems with this setup?
I don't see an issue with that, but I don't have any experience with that.
-edit-
Should I have any reservations at all about switching to an ATI+TH2Go setup from NVIDIA?
I don't think so. I tried my old DTH2Go on my original 5870 somewhere around the 9.12 driver. It would set up the 3840x1024 resolution, but not the 5040x1050. Considering you're running at 3840x1024, you should have no problem.
-edit2-
OK this worries me a little:
ATI Eyefinity multi-display technology2,3
* Three independent display controllers
o Drive three displays simultaneously with independent resolutions, refresh rates, color controls, and video overlays
SOURCE
You're not actually using the Eyefinity technology, so it shouldn't be an issue. Eyefinity is running the multi-monitor directly off the 5850, without the DTH2Go.
So is Eyefinity required for ALL multi-display configurations or will my proposed setup work with XP?
There are Catalyst drivers for XP, but you won't be using EF so it's not an issue. I actually hadn't seen the issue about EF not working in XP. Been a while since I ran an XP install.