http://www.jtsprockets.com/catalogue/part/JTR210/
This is what JT offers for this application. If you want to preserve more low speed controllability off road, consider 44. Frankly, I don't like taking my 6 speed Temp X on the highway, and I have a 39 tooth sprocket on that one. Plenty of power to push over 70mph. But for me it has nothing to do with the gearing. It's the traffic and high speed pressure from goofy drivers. I prefer two lane roads. I may just sell the 6 speed. I am more off road oriented, and will just take a car on the highway
BTW- I kept the 49T rear sprocket and original chain on the 5 speed. You can keep it stock for a while during first few engine hours and get the feel of it off road. That low gearing is nice for slow speed negotiation, and easy front tire lift on bumps. Wheelie fun
