Basically there no AMD CPU can equal an Intel Core i5-2500k.
See below link that compares the quad core i5-2500k to the quad core Phenom II x4 980 BE
http://www.anandtech.com/bench/Product/288?vs=362
The i5-2500k beats the PII X4 980 BE in every single benchmark except SYSMark 2007 - Video Creation benchmark. The PII X4 got scored 252, the i5-2500k scored a "measly" 251. However, I tend to ignore synthetic benchmarks since they do not necessarily release real life performance.
See below link that compares the i5-2500k to the 6 core Phenom II x6 1100T
http://www.anandtech.com/bench/Product/288?vs=203
The Phenom II x6 beats the i5-2500k in only one benchmark and that's the 2nd video encoding pass using the x.264 codec (presumably using Handbrake). Some benchmark scores are close, but many are not.
Below is the i5-2500k vs. the 8 core FX-8150
http://www.anandtech.com/bench/Product/288?vs=434
The FX-8150 also performs better in the 2nd video encoding pass using the x.264 codec. But it also does a bit better with most of the 3DMax benchmarks. It also does very well with POV-Ray 3D rendering benchmarks and edges out the i5-2500 in the Cinebench test as well. If you compress a lot of files using 7-Zip, then the FX does better there too. The 4 extra cores can come in handy in certain applications. There are a few other benchmarks where the FX-8150 does a bit better than the i5-2500k that I did not mention.