I actually only ever display games on one of them, but who knows what kind of setup I'll get in the future.
I think you're right, the 780s have 3 GB at the lowest, and there are 770s with 4 GB. Would you rather get a 4 GB 770 for 3500 arbitrary currency units (ok, Swedish Crowns :P) or a 3 GB 780 for 4000?
Thanks.