I do know going from 400 to 401 mhz causes a HUGE drop in memory performance. and from what it seems the multiplier seems to change the true frequency the northbridge runs at according to a few programs out there.
Yes I can show you that much. SiSandra shows my FSB at 400mhz, NB at 444mhz and RAM at 400mhz, 8996mbs. If I raise the multi back to 10x, the NB speed drops back down to 400mhz, and RAM mbs drop to ~7600mbs.
Also, CpuZ reads the latency of [9x, 400mhz] at : L1- 3 and L2- 16...while at [10x, 400mhz] it is L1-3 and L2- 13. So the latency improves, but the speed drops as you raise the multi. Lowering it has the opposite affect.
This does not answer, if 'speedstep' actually changes the strap on the NB when IT lowers the multi for power savings.