i would think it depends on your mods, and if you are auto or manual.
i am manual, and when i was stock, i didnt feel like anything above 6500 rpms helped me move anyfaster. now that i am modded, i take it to redline in both 1st and 2nd, at 67-6900 i shift from 3rd to fourth, and then milk fourth for all its got. fourth can get u upwards of 120+
it all depends on your mods, and your experiences with your ride.