The big question is how much power can your wallet produce?
I doubt that even with unlimited funds the 6.5 will not be a Dmax slayer.
I personally love the 6.2/6.5 for what they are.Cheap and easy to keep running.Cheap on fuel.And reliable if you don't try to hot rod it.
90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews