Depends on how much of the overly-tall stock gearing you want to retain, as some riders take the bike on the freeway a lot and want to loaf (lower cruising RPM) the engine on the open road.
Myself, I ran 12/45 on my 2008 WR250R, and it suited me.
That's close to 13/48 if you don't want to go with a smaller-diameter front sprocket.
In the end, you'll have to experiment and decide for yourself.