Spectek should be ok at 166MHz, but my two top out around 193 MHz (2.5/7/3/3 timings). Most of my PC2100 sticks reach higher speeds (Kingston, KByte-Me, PNY, 200Mhz +). The PNY PC2700 from Staples last month ($10 AR/AC) turned out to be Samsung sticks, and can hit 218 MHz.
Spectek is their low-end ram. Supposed to be good chips pulled from bad dimms, or marginal chips that don't get the Micron brand. Mine are 8 months old, so maybe current stuff is better.