Just ordered a tall Guard 5th gear .667
I have given it a lot of thought as to whether to get the Ring and Pinion also (Albins 3.1). The spread of gained MPH and lower RPM was more pronounced in the higher RPM/MPH range. My goal was to lower rpm in the comfort area for cruising and the tall 5th seemed to be the answer. If money was not an issue I would have done both. For now just a tall 5th.
I also found a really nice online gear calculator:
Gear Ratio Calculator | Weddle Industries | High Performance Driveline Components for Race Vehicles | Off-Road Transaxles, Clutches, Gears