18 amps per 12v rail. 4 seperate 12v rails. Im running a 5870 now off of two of the rails with no issue. Here is a review of the PSU. The review is old I know, and maybe the age of the PSU will be the biggest factor. It's 5+ years old now, and has been stable/without issue since it was bought. http://techgage.com/article/thermaltake_toughpower_modular_750w_psu/3
Here is the PSU description/specifications from the Thermaltake website: http://www.thermaltakeusa.com/Product.aspx?S=1207&ID=1502#Tab1
I used their PSU calculator and with my config the 750w TP was one of the recommended PSU's for my clocks(cpu) and xfire 5870's. So I think it would be fine, except maybe the age might play a huge factor. I'm not really sure.