Please do not try and inform someone, who came on this site to learn something, when you have absolutely no idea what you are talking about. Whatever you may define a "core" as, the FX-81xx has as many "cores" as Intel's 8 "core" Xions for servers. Hyperthreading on an i7 ,as far as I know, does not change any physical properties to the chip. If you want to look at a die shot of an 8 "core" bulldozer and tell me there is no physical difference between a FX-41xx and a FX-81xx, go right ahead, but your wrong.
The module approach of Bulldozer puts two "cores" together, having them share certain parts that are not always used. Each and every "core" is just as powerful as another, but when the two "cores" of a module work together, there can sometimes be losses in performance compared to if the two "cores" were separated.
To answer the OP's question: Yes, you will probably run into bottlenecks if you keep that clock speed. Not a whole lot with a single 670, but with them in SLI that will change.