My first summer is the Valley I climbed alot with a guy who climbed primarily at the Gunks. He climbed fine except he was really wanting at crack climbing, which he freely admitted.
Having said that, it probably depends on the route you're looking at and the type of climbing it involves. I hope this doesn't sound elitist, but if you're climbing 5.7, that probably should be fine since a 5.7 crack will likely have lots more edges and other features that you can exploit rather than forcing you to climb the crack exclusively the way, say, a 5.10 crack in the Valley might.
What routes were you looking at? Many of the people who've responded to this thread may have climbed the routes you're considering.