DPMS is an American rebrand of JG, and G&G is Taiwanese like ICS and LCT. You're most likely better off with the G&G, as their average quality and quality control is better than DPMS. Like venture said, best thing to do is get age verified. If you're not old enough to come to proper games then having a gun will be a bit useless, even for 'backyard battles'. It gets boring fast.
To answer your question, the smoked receiver G&G's shoot between 300 and 330FPS, from my estimation (which is hardly reliable), but perhaps a member who actually owns a chronograph can help out here.