Not necessarily. The R9-270X is much weaker than a GTX 760. The R9-270X is weaker than a Radeon HD 7950 but the GTX 760 is stronger than the 7950. Also, you chose the LE version of the motherboard so you won't be able to overclock the 8320 very good, if it all.
I'm not sure how much of a performance increase Mantle will provide as it is still not released yet, so that is still unknown. Nonetheless, the GTX 760 is stronger than the R9-270X.