I'm prob the only guy on here with this opinion, but if I was doin what you are doing, again, I'd get a nasty port on my stock cylinders and true and weld the stock crank. Unless I find a smokin deal on GOOD 4mill crank. If that wasn't enough maybe do a stock stroke serval. But like I said that's just me. I've been running a 4 mill for a long time but that's because I got a deal on crank, pistons, and ported cylinders. If you think you'll actually ride it with the mods you plan to do for a while and not make it crazy unridable in the woods I'd keep the stocker. If you think one day you'll be wanting a 100 hp bike like everybody else then do it while it's apart.