I have .02 on this one. Stock is 14/47 or 3.35-1 final drive. I think this will give you a top speed in the mid to high 80's.
I ride a lot of single track and woods. 14/47 is too high for what I do. I have a 13/48 which is a 3.69-1 final drive. This is right on but the chain rubs against the case at the pinion sprocket so it is not a good solution. A 14/51 would give a similar 3.64 final drive without the case rub issues. Having an extra 15 tooth pinion sprocket would give the option of 15/51 or 3.40 final drive slightly lower but similar to the stock 14/47.
Using a 51 rear and having 14 and 15 tooth pinions would give similar ratios to stock giving a top speed of probably 80 mph or so, and an awesome woods gear without case rub issues. I have not researched issues with the 15 tooth pinion but I bet it doesnt rub against the case! Size the chain for the 15/51 and you should have a winner unless you need to go faster!
This is my plan. Lytle racing group has some value o ring chains that have been working ok for me. They will size the chain for bike and ratio. Hope this helps.
Fitz