Cracking Speed: R290X vs. R290

I'm thinking about getting back in... Now, considering the significant differences in price (at least where I live) between the R290 and R290X models, and the fact that i'm looking into rocking between 4 and 8 of these units sometime within the next 3 months, I'm interested to know if anyone with experience can tell me if it's worth rocking a 290x rather than the 290. As I understand it currently, their performance is virtually identical except for the presence of fewer enabled cores on the plain 290.

Obviously we're not interested in gaming performance over here, so how does this translate into cracking performance?

290? or 290X?