is 768p higher than 720p



will there be any bottleneck or lag with my resolution
Build
gigabyte ga h97m d3h
antec earthwatts 650w 80+bronze
seagate 1tb hard drive
intel i5 4590(getting soon)
kingston hyperx blue 8gb 1866
win 7 64bit ultimate sp1
 


No worries whatsoever. Excellent CPU/GPU pairing. My recommendation for W10 stands though. Seeing as DX12 is W10 exclusive, if you want to play future games, you don;t really have a choice anyway.
 


will it be problematic if i dont upgrade to win 10 and game on win 7
 


Yes. You would not be able to take advantage of the added performance from DX12 mode in current games(which is substantial with an AMD GPU) and you would not be able to play future games that are DX12 only at all.
Not a good idea, especially since W10 is a far superior OS anyway.