I'd say that depends on the OC speed and voltage level of the kernel and other things like if you're using live wallpapers, lots of widgets doing things in the background, etc.
I suppose the ROMs themselves could affect battery life, say if one has more efficient code than another, but the stuff I said above would probably have a much greater impact. I.e., a ROM using a ULV kernel overclocking at 800 MHz would probably always lead to better battery life than one using a MV kernel at 1.2 GHz.
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Gingerbread really eats up the battery on the X, especially the first leak. It has been better since I installed Gingeraid 4.1 ROM.
As for Froyo, I had terrible battery life with Liberty 1.0 and 1.5. I never tried the latest one. Rubix used to be my favorite until he started using the same base as Liberty.