In most cases, V-RAM is not an issue but in your case it may actually be hindering your performance.
Are you adverse to purchasing AMD cards? If not, their offerings may be right up your alley. They are great for multi-monitor gaming and most of them are equipped with large amounts of V-RAM. You may actually want to look into a single HD 7970 at first, then add another one in the future if you are not satisfied with just one.
nVIDIA will release their high-end GPU's sometime in the second half of 2012 (rumor) and I believe they will be better performers. The only problem is the wait, if you can wait then I would recommend a single GTX 680 (or 780) and adding another one down the road if you are unsatisfied.
Lastly, if you do not want to purchase from AMD and you simply cannot wait, then a single 3GB GTX 580 is still a potent card and will be for quite some time. You simply can't go wrong with it. Some people will consider it a waste of money because they may be more expensive than the HD 7970 and perform about 20% worse in most games; keep in mind though that the 20% difference is usually less than 10 frames and sometimes it doesn't even matter because both of the cards blow past the magic 60 FPS number anyways.