965 BE. Quasi-quad FX can't keep up without being clocked 20% faster. That means a 4.0 PII would need a 4.8 ghz FX-4xxx.
For the record, AMD says that a single Bulldozer module has around 80 per cent of the performance of two conventional CPU cores. In other words, a four-module Bulldozer core should be at least as quick as a six-core processor.
Absolutely a Phenom II is a better CPU all around. I'll take 4 real cores to 2 cores +2 pretenders any day.
The FX uses less power at stock clock rates, however they get very hungry when you start overclocking. Either way though, in terms of your electric bill, the wattage difference of CPUs is pretty insignificant.