No need to go above 1ghz because the heaviest game on android is asphalt 6 i believe and then you have dungeon hunter II but i wouldn't recommend you to go anywhere above 1ghz as it risks your CPU's life and affects it. You can try overclocking to 1.2ghz only if you want to try out NDS4DROID lol.
Playing Dungeon Hunter II and Asphalt 6 without any lag in 1Ghz (300/24, 600/36, 1000/56 @80 threshould). Only take care with undervolt, if it's too low the phone will reboot.