The 270x is is not "the new on the block". It is a rebranded and updated 7870 with nearly identical 7950 performance.
To the op, I have a 270x it plays almost all games on ultra at 1920 x 1080. But that still does not change my recommendation of going with the 760 as it is still more powerful. The 270x was in my budget, and if you can swing a 760. Then by all means, I recommend that you do it.
R9 270x would be better in near future because of AMD mantle it boost the gpu 50%
Actually, Mantle focuses more on bumping up the performance on low-end CPU's than GPU's. With the processor this guy's getting, it'd be probably a 10% increase. If he were to get, say, an i3 processor of some kind, the performance increase would be pretty amazing.