Fair enough on the case; I was just curious. Regardless, it wouldn't be the end of the world if the OP threw an extra ~$15 into the chassis if he wants something a little more substantial. I'm just impressed you crammed a 7870 into a $500 build.
SWTOR is kind of an odd duck. It's
so poorly optimized for large-scale multiplayer encounters that the developers basically nuked their big PvP battleground shortly after the game launched. So ironically, because the game is CPU bound when many other players are on the screen, there's almost no realistic situation in which you'll actually find a lot of players fighting together -- if that makes any sense.
FWIW, I've played the game a fair amount on a rig with an i3 3220 and a HD7850. The game is butter-smooth whenever I need performance (fighting either solo or in the small team encounters that comprise the vast bulk of the game's group content). In those situations, the game is GPU-bound; the game's native FPS counter even tells you which component is bottlenecking your system at any given time (numbers red if GPU, green if CPU).
The only time my CPU rears its ugly head is in the main hub area where there are lots of players standing around, checking the auction house and whatnot. In those areas, I can see dips into the 20-fps range, but then again my FPS doesn't really matter when I'm standing at an NPC vendor.
So the TL;DR on all of that rambling is that I don't think a beefier CPU will really make all that much practical difference in SWTOR as it's presently constructed. YMMV, caveat emptor and all that jazz.
I don't have any direct experience with Diablo III. You make good points on all the rest