Depends on the resolution of the monitors. If you're going to using 1080 monitors, stick to 780Ti. If you're going for 1440 or 1600 monitors, you'll probably find use for the extra 3GB of RAM. Not many games can use that much memory without lots of texture mods and high levels of AA, but if you happen to play Battlefield 4, that's one game that can use up over 4GB at extremely high resolutions.
780ti comes with 3GB of vram. BF4 on ultra setting at triple 1080p uses 3.2GB. It will still run it but it's right at it's limit. Future games on the other hand may be an issue. That's actually the reason I haven't bought one yet. If it's two monitors, the 780ti is the best out there right now.