There are probably two things you should consider before anything else.
For Eyefinity, you'll need at least one monitor to have a DisplayPort connection or you will have to use an active DisplayPort adapter. Sounds like you're already in good shape in that regard. If you have a native DisplayPort on your monitor, you will not need an adapter. Any card in the 5XXX series or higher will technically support Eyefinity on a single card.
For NVSurround, you'll have to make sure that all the monitors have the same sync polarity. From my experience, this can be tricky. Almost no sellers list the sync polarity on their monitors and you may have to search around for a technical manual on any models you're considering to find their sync polarity before purchasing. Any single 6XX series Nvidia card will technically support NVSurround. 5XX series cards will support NVSurround, but only if you have 2 of them.
I've used both the 5870 and 7950 models from AMD in Eyefinity and generally been pleased. If you can find one still for sale, the 5870 shouldn't have any issues running older games in Eyefinity. HL2 and IL2 will certainly work well. You'd probably have no trouble with ME1 and ME2, but ME3 would be pushing it on a single 5870 in Eyefinity. Something newer like Battlefield 3 would probably require you to drop all the settings down to low and you might still be struggling to get playable framerates (I ran Battlefield 3 on 2 5870s and still had to drop my resolution from 5760x1080 down to 4800x900 and put all my settings down to medium or low for competitive play.)
One issue that exists in Eyefinity but not under NVSurround is screen tearing. If you're not using three identical connections in Eyefinity, one or more monitors may have tearing. Here's a Wikipedia article on the subject with a pretty good example of what it looks like:
http://en.wikipedia.org/wiki/Screen_tearing. Using 1x DisplayPort and 2x DVI on my 5870, I never had any screen tearing. On my new 7950s I'm using 1x mini DisplayPort to DisplayPort, 1x DVI, and 1x HDMI and I do get tearing on my side screens. It's a little annoying, but your mileage may vary. I think it's the kind of thing that some people won't care at all about and others can't stand. If you're bothered by screen tearing when playing with VSYNC turned off, Eyefinity tearing will probably bother you even more.
Since I only have experience with AMD, I don't want to comment too much on NVSurround. But, word on the street has been that NVSurround has matured to the point that it competes well with Eyefinity and does quite a few things better. I'm pretty sure several WSGFers have switched from Eyefinity to NVSurround and been pleased.