Well it shouldn't be any problem except that both cards have to have the same clock speed.
I think the iceq turbo x is clocked at 970, vapor x at 900. So if you cf the iceq clock will be lowered to the vapor x.
You can then oc them and try get them both to 970.
If you don't already have the vapor x I'd get another iceq turbo x and cf them