It's still the same question, and the same answer. GTX 960 (Any)>R9 280. R9 280x > GTX 960.
2GB or 4GB doesn't matter. The GTX 960 Maxwell architecture doesn't utilize the additional VRAM to any great benefit except on a couple of games, or if using SLI, which makes no sense because for the 400 bucks it would cost for GTX 960 SLI you could get a much better single card with none of the dual card issues that plague many current titles.
I personally would rather spend my money for the R9 280x than the GTX 960. The R9 280 is a good card too, but it does not win on very many titles versus the GTX 960 in most configurations.