The problem is the gigabyte board lacks VRM for the CPU, which is going to be more power hungry, than Intel's IGP. Those VRM's are more likely to thermal throttle, limiting turbo clocks.
for start, i will use a sapphire video card ati R7-240 2gb / ddr3,
I know this video card doesn't have uefi, will I be able to open the pc with the asus motherboard?