Please help with gaming pc build

Solution
I would say replace the 770 with a 290. Here are some reasons why to consider the 290 over the 770.

Significantly more memory 4,096 MB vs 2,048 MB 2x more memory
Significantly higher pixel rate 60.6 GPixel/s vs 33.5 GPixel/s More than 80% higher pixel rate
Higher memory bandwidth 320 GB/s vs 224 GB/s Around 45% higher memory bandwidth
Better floating-point performance 4,800 GFLOPS vs 3,213 GFLOPS Around 50% better floating-point performance
Better 3DMark 11 graphics score 14,570 vs 11,310 Around 30% better 3DMark 11 graphics score
Significantly more energy-efficient idle power consumption 87W vs 109W More than 20% more energy-efficient idle power consumption
Significantly more render output processors 64 vs 32 Twice as many render...

firo40

Splendid
I would say replace the 770 with a 290. Here are some reasons why to consider the 290 over the 770.

Significantly more memory 4,096 MB vs 2,048 MB 2x more memory
Significantly higher pixel rate 60.6 GPixel/s vs 33.5 GPixel/s More than 80% higher pixel rate
Higher memory bandwidth 320 GB/s vs 224 GB/s Around 45% higher memory bandwidth
Better floating-point performance 4,800 GFLOPS vs 3,213 GFLOPS Around 50% better floating-point performance
Better 3DMark 11 graphics score 14,570 vs 11,310 Around 30% better 3DMark 11 graphics score
Significantly more energy-efficient idle power consumption 87W vs 109W More than 20% more energy-efficient idle power consumption
Significantly more render output processors 64 vs 32 Twice as many render output processors
Slightly better 3DMark06 score 32,300 vs 29,690 Around 10% better 3DMark06 score
More shading units 2,560 vs 1,536 1024 more shading units
Significantly wider memory bus 512 bit vs 256 bit 2x wider memory bus
Higher texture rate 152 GTexel/s vs 134 GTexel/s Around 15% higher texture rate
More texture mapping units 160 vs 128 32 more texture mapping units
Higher BioShock infinite framerate 91.5 fps vs 83.4 fps Around 10% higher BioShock infinite framerate
 
Solution

firo40

Splendid
mantel and direct x are API's they basically allow games to utilize your graphics hardware. Direct x is owned by microsoft and is the standard. Mantle is new and developed by AMD. Mantle is suppoused to allow amd gpus to perform better but the results have been pretty lacking and alot of people say the textures are washed out compared to direct x. I expect Mantle will get better in the future though