Ian, The way I look @ it is where do you want the power, I run old 59* factory blocks with W5 heads so @ 414 inches we run outa breath over 7k & the block and valve train don't seem real happy higher , WE can pull to 7500 with a small roller 260@ .050 .685 lift 106 0n 106 but the real hard pull is down around 6 to 6800, In the mud the resistance will pull the engine down fast so a higher TQ, shorter power band seems to work better for us, We ran larger rollers with wider spreads 109 , 112, and had problems turing larger more aggressive tires requiring more gear & converter thus reducing wheel speed and having to turn more rpm to compensate, The shift recovery is also faster with the shorter power band. The Nos guys in the mud seem to favor 107-108 advanced 4 with a boatload more exhaust duration @ least 10*+, To have a setup that runs Na and Nos and not favor one side is hard to do, seems ya gotta trade a little somewhere.
