I'm running right around 2K @ 65 mph right now with a 25.6" tire, 3.21 gears and an A833OD. My expectation when I swap to the 5.7/T56 is 3.55 gears with a similar sized tire and 1500 rpm @ 65 mph, duplicating the rpm's my old '15 R/T ran.
My only point with my previous post was that the A8 could potentially introduce some new problems. If you put it behind a rowdy motor and expect it to cruise at 1500 rpm, your motor might not be happy at that rpm. And if you gear it so the highway rpm's better match your motor you can end up with 1st (and maybe 2nd?) gear being completely unusable. Or maybe you end up with a 7 speed trans because 8th is only useful on certain highways, or the Autobahn.
The 8A spreads the usable rpm's so far that the motor can start to be an issue, in my opinion. Just seems like EFI becomes more important so the motor runs smooth on both ends of the torque curve, or maybe a mild motor is better fit. Personally, it's one of the reasons I like the G3, it makes good power as a 5.7 and more than enough as a 6.4, but both are still efficient at 1500 rpm.
Not to say that there aren't wizards out there that could build a 500 hp 408 with a carb that can run smoothly under load at those lower rpm's. Just that it seems like the big HP usually came at the expense of low rpm drivability which seems like it could cause problems if you are asking the motor to spend a fair amount of time in those lower rpm's.
Just something to think about.