A better air cooler might improve your temps anywhere from a couple degrees to 10c or so under load. There are plenty of good air coolers, the nh-d14 mentioned, the phanteks tc14pe, dark rock 3/pro 3, cryorig r1, thermalright true spirit 140 power (if it will fit your case, it's 170mm tall). Just my opinion, aio coolers seem to be problematic more often than not. The single radiator versions rarely perform better than decent air coolers but offer a different look (less clutter of a cooler on your cpu in the middle of the system if that's an issue). Dual radiator coolers would be more worthwhile given the cost of aio's.
You can try a different fan on the 212 evo but keep in mind before investing a ton in fans (most decent fans are...