to be honest i din't know how FPS overcloking my GTX 770 adds. never compared it. on;t reseaon i overclocked it was because i could
As to get the Gigabyte or MSI it's up to you. i only picked the MSI because or it's red and black colour scheme which matched the rest off my build. both cards have good cooling and run quietly. so pick the cheapest or the one you like the look off best
oh quick after thought. the MSI gtx 770 need 2x 8pin PCI-E from your PSU but does come with 2x 6pin to 8pin adapters.
The gigabyte gtx 770 needs 1x 8pin and 1x 6pin. if that makes any difference depending on your psu