food for though...
while 0.50 OD sounds nice, you need the torque at that RPM to use it or the engine bogs. Think of the 10th gear on the bike going up a slightly incline, unless you have strength or prior speed, it will be tough.
for the cost conscientious, install a Richmond/ Doug Nash 5 spd , swap in 2.73 rears and call it a day. Still 1:1 5th but has a deep 1st to move from a stop. Could probably use 2.56 gears if you wanted. Can find all you need 2nd hand for under 1500. If I didn't mention a part, it is not needed for the swap. I run this in a 74 T/A back by a stout 455 w/o issues after 10k miles. I get 16-18mpg on highway cruising 2500-3000 rpm. speed is .03*RPM