The Hyper 212 Evo is about the best bang for your buck cooler. It will be fine for your Phenom II. Push/pull just involves mounting a fan on the back of the cooler blowing through ( stock set up ) and a fan on the front pulling. The dual fan configuration will lower temps maybe a few degrees. Most Phenom II chips top out about 4Ghz due to the limits of the architecture. A Hyper 212Evo with a single fan should get your CPU to 4 Ghz with no problems. Remember to keep max load temps under 62C.
62 is max before degradation but 55C is max before stability issues, running high overclock on 57C might cause cpu to bug out