Just an opinion as ultimately you will have to decide for your self............
If you are building a bar hopper and dont intend to travel any distance then lower gears will kill everything around you.
If you like to go on trips then 3.37 is pretty good for all round performance.
What gets lost here a bit, again in my opinion..........is that bikes like the Softail Standard FXR etc. can do quite well with the torque cams like the TW5 or 6H without the need to go to 3.37.
The Road Kings on up would do to have 3.37 and the torque cams to get them moving.
I tried to respond to your pipe idea but dropped out and gave up...as we get sh!tty connections over here quite often.....................the design looks great and would sell for sure.......................what has to happen is that you need to test it with a number of cam/head combos and work out correct distances from the head to the intersection and then after lengths........50" all up seems to work on my computer quite well, but pipes like 2:1`s etc. always get dips in the curve that I can not take out using this software, that obviously can be in the real world, and 1 company is stating on their website that 12 degrees is what the angle should be when the pipe leaves the horizontal and turns down to meet the lower pipe and visa versa.
Then patent it, sell it with baffles and let the rider be able to take them out and then when you make your first million.........remember me!! ha!!
All the best, Ozzie