I think capping is a little much with this many people still in the hand because youre not protecting your hand at all. Plus a person with a .6 aggression factor 3 betting the flop is kinda scary, but I dont know how many hands you have on him. I would call the 3 bet and evaluate how you can protect your hand on the turn. Since you bet the turn I would just call down if raised and you dont improve. Obviously a diamond could make things a little scarier