You cant OC onboard, they're either scam or PCIe, there's 0.00000000% chance of even Overclocking it... you probably saw a 7660 being OC which are PCIe 2.0 on desktop, not sure if there's 7660D that's overclockable if it's onboard... If you want better GPU performance, get the product ONLY if you have thunderbolt built in
https://www.youtube.com/watch?v=oO1Ze5JXnFk