Six cylinder engines really don't respond like a V8 does when X pipes are installed, a simple H pipe will do the same if you want to save some money.
As far as pipe size goes, keep it small since you are running two of them. Your engine will not produce any more exhaust then a stock engine does as long as you drive it like a stock truck. Higher rpm is the only way to make more exhaust, the intake and headers will only let air in and out easer, not produce more.
With that said, 2 2" pipes will be plenty, smaller pipe will hold heat in which lets the exhaust flow faster, it slows as it cools.
Joe
