the 2-speed in my 58 2-ton has 6.4 and 8.75 ratios. I have 9r-22.5 tires and an SM420 (predecessor to your SM465) I am spinning ~3600 to go 60 down the freeway and 4200 to go 70. Not sure what the newer 2-speed ratios are or what tires you are running but the 2-speed may get you a little more speed per RPM.
