Since no one sells the 768 anymore, the point is moot. Good luck finding one....

768MB of VRAM is going to be a issue with the high resolution multi monitor brings with it. Even though the monitors by themselves aren't super high resolution, when you combine them you end up with a resolution of 5040x1050. That is going to eat through 768MB of VRAM very quickly and you will likely have to turn down settings like texture resolution, AA or post processing effects to try to keep under your 768MB VRAM cap.
 
In case you didn't know, adding additional cards does not affect how much VRAM you have available for games. So 2 768MB GTX460's do not equal 1536MB VRAM. Since for SLI to work all data that's in one GPU's memory must also be mirrored in the others. That gives you a total VRAM equal to one card.
 
If you're thinking about trying out multi monitor, I would advise at the bare minimum 1GB VRAM cards. I would suggest trying to sell your current card and move up to something with more memory. If you look you can find the 2GB GTX460's for decent prices. 2 of them in SLI would make for a pleasant Surround experience on a budget.

fleetingyouth

Thanks for the tips craptacularone. Now im not sure what to do.

I did know that the ram doesnt stack but i figured it not being 1080p it would be enough.
would I see a big difference if I had 2 1gb versions?

Anything bigger just isnt worth me upgrading to at this point.

Just because the monitors aren't 1080p doesn't mean anything when you're talking about multiple monitors and surround screen gaming. You'd see a appreciable difference with the 1GB cards at 5040x1050 but still may have to dial some settings back in the latest games. If not playing at the utmost image quality settings doesn't bother you, then go for it. The 1GB GTX460's are dirt cheap and will give you an extra 256MB VRAM.
 

I have to disagree, a minimum of 470s is not required.  I'm running a 3 monitor setup on a GTX 460 2Win 2GB card, 3 23" monitors in 1920x1080 each (5760x1080 before bezel correction) and am not seeing performance losses that make games unplayable.  He's right when he says the 768MB of VRAM isn't going to be enough, but it's not just the VRAM amount, the 768MB cards also have 192-bit memory interfaces rather than the 256-bit memory interface, meaning there are fewer active memory controller units.  This will also have a bit of a hit on your performance in this kind of setup. 

Thanks guys. I think ill grab a friends 2 1gb 460's an see what results I get. Like I said I dont play a lot of demanding games But I know Skyrim would probably be pretty demanding.
 
Im not interested in dumping a ton of money into setting up 3 monitors this was mostly just for work so for that it works if I can play games with 2 1gbs then Ill do that otherwise illl just stay one monitor for games.