If you were to load a mobo with a phenom 9900,...(extrapolating the b3 stepping) and a mobo with a QX9750,...both running the,....3879x2,...would the cpu make a difference at all? Supposing all other hardware was ample!
Considering you will have a unlocked multi and a stock speed of 3.2GHz the OX9750 will basically be able to be OC'ed nicely and give an advantage in certain games like Supreeme Commander, HL2 Episode 2, TF2 and Crysis.
Or FSX. Still, most games will behave the same with either of those CPUs because the video card and the hard disk are limiting factors before the Phenom reaches its max.