Cleft Asunder: I've often seen people (usually people who don't care about fuel economy) claim that "my car gets better MPG at higher RPM", yet I've
never seen any attempt to provide credible evidence.
Pretty much anyone who has spent time with fuel economy instrumentation will tell you that shifting to a higher gear
whenever possible will reduce fuel consumption for a given road speed - right down to the point of lugging the engine. That's been my experience in every car I've driven, anyway.
If I were you, I'd go ahead and do the VX final drive swap.
FYI, I did a swap where I reduced my RPM by
25.6% compared to stock (
Project 'nerd gear': taller tranny transplant nets +5.2% MPG - MetroMPG.com ). That's a massive change. And it improved fuel economy.