PC3200 will also work, but may not get much extra speed, depends on the mobo you use.
PC2700 is is matching 166mhz speed.
PC2100 will work if you force the mobo to run the ram at 133mhz.
You might be able to get better prices on PC2100, and most workstation users won't even notice the difference. Might save a bunch of money for something else, like maybe cd burners or something.