Yeah, I second a GTX-760, though a GTX 770 is the way to go if you can spend the $ for ARMA3. I actually run 770 4GB SLI for ARM3 now, bought (1) 770 last year and then I picked another up last week. It was a huge jump in FR for the move to (1) 770, a 2nd just helped steady out the variance I was seeing with (1) card.
2GB is fine for single-monitor 1080p, go 4GB if you are going to go above 1080p to future proof your investment.