Seems 4gb of VRAM is now the minimum if you want to run everything maxed out, even at 1080p.
Call Of Duty Advanced Warfare, never ran that on the 780 Ti, but maxed out at 1080p it uses about 3.8gb VRAM and runs silky smooth.
Did buy 2x Reference inno3D GTX 980's but found in SLI with a single slot spacing between the two, it ran hotter and downclocked far quicker than my EVGA Reference GTX 780 Ti's.
My 2x reference 780 Ti's would pretty much stay at their full boost speed of 1020mhz (stock 876mhz) 80% of the time, even with hours of gaming. The 2x GTX 980's downclocked from their max boost speed within minutes. I even changed the stock paste to Coollaboratory Liquid Pro, helped a little but not much. Looking at reviews it seems that Nvidia didn't use the vapor chamber cooling on the 980, that probably explains the hotter temps.
So I replaced them with 2x Gigabyte GTX 980 G1 Gaming.
These run much cooler. These boost to 1367mhz from the stock 1228mhz and they stay at their max boost clocks permanently during gaming/benching. 8hrs of Call Of Duty Advanced Warfare, maxed out at 1080p, bottom card stays around 58c (39% fan speed), top card 68-71c (50% fan speed). Extremely impressed with these cards. When idling they are around 1c to 3c apart. I did replace the stock paste on both with Coollaboratory Liquid Pro as one card was idling 7c hotter than the other one. The stock paste on the Gigabyte was crap, it was very dry like cement, came of in 3 large chunks. The stock paste on the inno3D though was very good.