I verified yesterday that the chain I have on (2 links longer than stock) works with 15/50. In theory, that would lead me to believe that 15/48 would work on the stock chain (2 less teeth, 2 less links.)
I did a little running around with 14/50 last night and I can now stand the bike up in fourth gear up to ~70mph but find the rev limiter in sixth somewhere around 90 (on a closed course, of course!
Starting to feel like an MX bike having to shift so fast! I can be in sixth without feeling like it's gonna stall by 45mph, 70mph is roughly 6000rpm now.
Edit: It was eating me up not knowing how long the chain was so I went to the garage and counted 116links, so stock was 114.