[data from a 700/550 MHz Pentium 3 with speedstep]

[at 700Mhz]
PERFCTR INIT: vendor 0, family 6, model 8, stepping 3, clock 696920 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 209 cycles
PERFCTR INIT: rdtsc cost is 34.4 cycles (2413 total)
PERFCTR INIT: rdpmc cost is 34.4 cycles (2415 total)
PERFCTR INIT: rdmsr (counter) cost is 91.2 cycles (6047 total)
PERFCTR INIT: rdmsr (evntsel) cost is 72.6 cycles (4861 total)
PERFCTR INIT: wrmsr (counter) cost is 80.5 cycles (5365 total)
PERFCTR INIT: wrmsr (evntsel) cost is 75.9 cycles (5069 total)
PERFCTR INIT: read cr4 cost is 1.7 cycles (320 total)
PERFCTR INIT: write cr4 cost is 42.0 cycles (2901 total)
PERFCTR INIT: sync_core cost is 106.7 cycles (7043 total)
perfctr: driver 2.7.9, cpu type Intel P6 at 696920 kHz

[at 550Mhz]
PERFCTR INIT: vendor 0, family 6, model 8, stepping 3, clock 547735 kHz
PERFCTR INIT: NITER == 64
PERFCTR INIT: loop overhead is 197 cycles
PERFCTR INIT: rdtsc cost is 32.8 cycles (2299 total)
PERFCTR INIT: rdpmc cost is 34.5 cycles (2410 total)
PERFCTR INIT: rdmsr (counter) cost is 91.4 cycles (6047 total)
PERFCTR INIT: rdmsr (evntsel) cost is 72.8 cycles (4861 total)
PERFCTR INIT: wrmsr (counter) cost is 80.7 cycles (5365 total)
PERFCTR INIT: wrmsr (evntsel) cost is 76.1 cycles (5069 total)
PERFCTR INIT: read cr4 cost is 1.9 cycles (320 total)
PERFCTR INIT: write cr4 cost is 42.2 cycles (2901 total)
PERFCTR INIT: sync_core cost is 106.3 cycles (7002 total)
perfctr: driver 2.7.9, cpu type Intel P6 at 547735 kHz