Umm, no, first of all, there is no FSB on AMD Procs (hasn't been for a long time). The ONLY differences between the 9850 and the 9950 is the multiplier which is 13 instead of 12.5 and is a 140 Watt part.
HyperTransport != Front Side Bus. The CPU multiplier on AMD processors refers to the HT "base clock" (whatever that means) which is set at 200MHz for all models (not 266). Thus raising the CPU multiplier doesn't involve raising that base clock value, and the HT frequency remains at 2GHz for both the 9850 and the 9950 (1.8GHz for all other Phenom CPUs except the "power efficient" 9100e, set at 1.6GHz). The only thing that changes is the CPU's frequency (which would be 200 x 13 = 2.6GHz exactly, not 2.66).