Probably pretty close between capping\folding. After 4300 hands, I don't think you're doing tremendously well against his 3 betting range combined with a 12% UTG raise.

Being out of position on the flop really sucks. If you don't hit your ace or king you will have a tough time playing the hand postflop, and there are the times when you hit your A\K and still lose a lot of money to AA\KK.

You might be losing a tiny bit of equity folding here (and I'm not even sure you are in this case), but you are certainly keeping your insanity level up and variance down.