A few things guys:

1 - the 7750 is faster than the R7 250.
2 - BOTH support mantle, every GCN gpu does.
3 - the 260X is a rebrand as well, it's a 7790
4 - get the 7750 thumb.gif

7750 at 800mhz is higher in 3dmark firestrike and Heaven 4.0 benchmarks:

Boost Clock: 1100 MHz, 2048 MB, GDDR3, 8.19 inches.
can be overclocked for a small gain. Works great on games
Doesnt require a big power supply recommened a 400w
Very good for a card that doesn't require additional power

Radeon R7 250 is a middle-class graphics card based on the GCN architecture.
It packs a core codenamed Oland XT, previously used on Radeon HD 8670 (OEM). Therefore, it offers 384 Shader Processing Units, 24 TMUs and 8 ROPs, on a 128-bit bus width of fast GDDR5. While the central unit runs at 1000MHz and goes up to 1050MHz, in Turbo Mode, the memory clock operates at 1150MHz.
Its performance is somewhat comparable to Radeon HD 7750, though the latter will perform better at DirectX 11 games. ...

need more from this price, please reduce the price , in below 3000 c ategory this is best average performance

buy a 7750 instead, its old technology in new package. No new technology involved. Even 7750 perform better than this and support mantle also.