Diablo III, isn't going to be a VERY PC intense game. I've helped build a couple people's computer's to ONLY max out Starcraft II, and I think Diablo III is built on the same engine. Your builds are MORE than enough for that game. From what I know SC2 is pretty much CPU capped after this point at 1080p and there's not much point in going farther than that.
People will always say the i5 2500k IS the better CPU than the 1100t (It is) However, in terms of price but they always forget to factor in the motherboard is still expensive for the intel brands. I play with a couple of guys who have a 1100t and have a Radeon HD 6970. They play BF3 on high/ultra with playable graphics.
If your looking to OC a little on a budget.. I usually recommend this CPU cooler:
Cooler Master Hyper 212 Plus: $30
In terms of PSU: I'd find a nice 600-650watt PSU from Corsair, XFX(New versions), OCZ.
(If your gonna play Diablo III and maybe a couple of other games like MW3 or Skyrim, you don't need to OC

Like, your gonna see a difference between 60+ fps.)