They all run on a 9x multiplier if I remember correctly, the difference is 0.1Ghz I think for each chip. i recommend the E2180, its a beast, On a cheap $20 Zalman cooler I got it stable at 3.4Ghz And its only cripple is the 1mb cache but that only makes a 7-10% difference, hell id take that for the 50-70% price difference
^Has no idea what he's talking about. Please don't spread fud.
OP, Your original assumption is correct, the multiplier is the only variable between them E2160 (1.8Ghz - 9x multi), E2180 (2.0Ghz - 10x multi), E2200 (2.2Ghz - 11x multi). All have identical cache, capabilities, etc.
However, he is right that they are ALL good overclockers (especially with a good cooler).