depends on the game...some games use a poweful gpu some use cpu some use ram(bf4) you should be able to run games but on lower settings(maybe mid) and check out the corsair builder series psu's
your cpu/motherboard may bottleneck the GTX750/660 full power however you will still get a performance increase just wont be the full power/performance of the cards
depends on the game...some games use a poweful gpu some use cpu some use ram(bf4) you should be able to run games but on lower settings(maybe mid) and check out the corsair builder series psu's