I would say get the 8120. Also those are easy to do a mild overclock on. just set up the bios to mimick the 8150 and 90% of the time it will run without even touching the voltage or any other settings.
end story, you get the best of both, speed and cores for the price of the 8120.
Not calling it ghz because thats not accurate. It all depends on how well the program utilizes separate cores or how well it responds to raw speed. For the most if you do not overclock at all, in theory they sould be really close in performance. but overclocked to 6100 speed, the 8 core will tear the 6 core apart.