<short version>
With an AMD card, in Extended Desktop mode you will be able to run each screen at a different resolution and refresh rate. However, in Eyefinity mode each screen needs to run the same resolution and refresh rate.
</short version>
<long version>
Eyefinity has to run all the screens at the same settings. It does this by duplicating the settings of the worst screen. If you run 2 x 1920x1080 screens and a 1024x768 screen, switch to Eyefinity and you'll be running 1024x768 on each!
I'm running a DGM L-2647WDH in the middle (1920x1200@60Hz) and 2x Iiyama E2409HDS's on the side (1920x1080@60Hz). Currently I've got a 7970, before I was running 2 x 5870's, the Eyefinity "rules" have been the same throughout. Just had a play, and in Extended Mode I was able to change my middle screen to 75Hz and keep the sides on 60Hz - my middle screen had to drop resolution to do it, but that won't be a problem on yours as your native refresh is 120Hz at full resolution.
When I switch to Eyefinity mode, Windows only sees one screen at 5760x1080 running at 60Hz. If I try to up the refresh rate, I would need to drop the resolution to 2400x600 as that is the highest setting my lowest spec screen can cope with.
</long version>
I don't know about NVidia's Surround and how strict it is with screens, but I believe it is stricter than AMD's requirements so I don't think that will work either. Hopefully someone with a working/better knowledge of NVidia Surround will chip in?
