With the sm465 at 1:1 4th gear,4.11 rear gear, and 35in tires...at 65mph you'll be turning 2565rpm...not terriblely high rpms but I try to keep mine around 2000rpms for extended highway cruise speed...
With a 6.0, you dont have to drive it heavy throttle (yeah right)...I cant...
Heres a rpm calculator that may help your decision...
http://www.csgnetwork.com/multirpmcalc.html