A 2 speed isn't really going to make much of a difference in top end and the low end will be the same (first gear in the 2 speed is the same gear ratio as stock 16/48). Toss that jet pro on it and go up 2 teeth on the clutch/pinion to an 18 and down on the spur 2 teeth to a 46. It will be (a little) less likely to wheelie off the line and have better top end. Great for parking lots. At full throttle it will still pull the front wheels with this gear.
The biggest problem with the 2 speed is getting the gear mesh straight and adjusted properly (It's a lot harder than adjusting the 2 speed on my old Savage) I had one, I hated it and went back to single speed... The other thing is, the 2 speed I bought was plastic, even if I had liked it, I would've had to replace all the gears with steel gears, another $150. I personally believe the 2 speed was made for on road. I think bashing in the dirt with jumps and what not will kill it..
Just my opinion, feel free to disagree

Trip..