So according to GrimmJeeeper.com, if I go with my NP435 3.73's and a 41" tire, I'm 24xx rpm at 80. If I go with a 37" tire, and a ZF-6, with my 3.73's, I'm 19xx rpm at 80.
Is it worth the $2800 entry fee to get into a ZF and t-case for a 400~ rpm gain at 80, especially at a 2" ground...