Assuming a fresh set of late model (hydraulic cam) valve springs and other wise stock valvetrain, I've seen valve float at 7400-7500 rpms. But with peak power being made at 5200 or so, even 6000 rpms is redundant with a stock engine. The exception being the horrible 2-3 gear ratio drop, so it makes sense to hang on a bit longer in 2nd gear.
HTH,
Bob
HTH,
Bob