Sorry for bumping an old-ish thread, but this was the only GTX 960-specific one I could find.
So from checking Newegg & Amazon, I guess the 4GB 960 models are finally starting to appear: EVGA has released a 4GB model at $240/$250:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814487128
This comes close to a sweet-spot for me, though I think the price is still a bit much: I only do 1080p gaming, so the 970 seemed like overkill, but I was also concerned with buying a 960 2GB since so many games seem to drive up VRAM usage with ultra and high textures, etc.
So... at this point I guess my options are to get a standard 2GB 960 for $200, a 4GB 960 for around $240, or a 970 for around $330... I'm leaning towards the 4GB 960 if I can maybe get a good rebate or promo with it.
P.S. I guess there's no indication as to whether these are "actually" 4GB cards or 3.5GB cards like the 970...