Well you will gain more bottom end and tons more mid range, as well as a motor that can run up to 80+ hp on gas if you set it up right.
I can let it pull in the midrange now, where as a stock stroke it would have died off the pipe completely.
What I would suggest is to call Kevin and have him give you a quote on what you'll need to put a good 4mill together. There are a lot of little things that go into it that are easy to overlook.
Plan on spending about 1200-1500 bucks in the motor, before suspension or anything else.
You'll need your stock cylinders ported for a 4mil, cylinders bore and hone, new top end (pistons) kit, 4mil domes, seal kit, crank (hot rods is the only way to go), etc.
Here is Kevin's page with his 4mil packages on it http://herrjugsracing.com/Porting_Motor_packages.html
Don't forget to get a pingel and remember to drill out your gas cap!