That Athlon II X3 (unlocked X4) would definitely beat the Q6600 in unbiased multi-threaded work loads but I'm not sure about single-threaded loads but I'm leaning towards the Athlon wining in that too.
Unlikely . The 6600 is the same architecture as later core 2 quads . Core for core , clock for clock they are roughly equivalent to Phenom ll processors
The athlon may be the same stars core as phenom but it is detuned . Unlocking it wont add cache