The most important spec is the MODEL as in a 760M is much better than a 740M.
I'm guessing the GK208 is a rebadged 600M series, whereas the GK107 is the newer GPU. Performance wise they're likely identical, however the GK107 would run COOLER thus fan noise should be less.
How well a 740M works for you depends on what games you play. Diablo 3 for example, isn't very demanding, but BF4 is a beast I'd never play on most laptops.