There's a lot to that question, but the basics are that more than 4 cores don't mean anything for gaming, the 8150 doesn't perform like a true 8 core CPU should (8 integer cores, but only 4 Execution units), and the Bulldozer architecture is much slower than Intel's Sandy or Ivy Bridge (IPC, like. Z1NONLY said).
You also can't compare speeds between them because the architectures are so different (and of course, they're from different manufacturers).
Main overall point: Don't be fooled by AMD's "more cores is best for EVERYTHING" argument and their claim that the 8150 is a true 8 core CPU. Very little main stream use for more than 4 cores, anyway (just in video encoding, mostly).