Lineron

it depends on the generation of your cpu, on amd ryzen platform higher clocks can make huge imapct on frames. on intel haswell generation the difference is very marginal within 1 fps, on skylake i feel its the same maybe 2-3 fps tops

All that you need is to actually read the boot key combinations... In your case hold option when turning it on and it will let you choose the disk to boot. I doubt it you fucked up the HD. More keys and explanations check https://support.apple.com/en-us/HT201255