Well best thing for you is to limit game to 60 FPS, you dont need more for GTA V.
I am using DXtory to limit my FPS to 60 to reserve power, also shouldn't his CPU still be at 100%?
Just use Vsync for that no need for DXtory.
He limited FPS to 60 and have CPU overclock with weaker GPU so ofc he wont be getting 100% usage.
You can use MSI LiveUpdate to check and update BIOS.