As high as you can till you start floating exhaust valves lol. You won't be making any power up that high with stock heads/cams, and especially so if you're not running any sort of power adder.
Look at the power curve and determine for that....about 6000-6200 for an auto with stock heads and cams and 5600-5800 with a 5 speed.......is where you will do the best at the track during shifting.......you need to stay where the power is not the RPM's.....about 6200 peak with stock cams at WOT.......with a good set of cams and springs....then you can rev much higher.....