I have a 99' 125 EXC, live in Wisconsin at about 1000' elevation.
My jetting is the stock main jet, the top clip on the stock needle, and a 45 pilot jet, 6.0 slide.
I used to use a leaner main jet but switched back to stock after losing a crank bearing. I also tried a 7 mm slide, didn't like it, although it seamed to clean up the bottom in conjunction with the 45 pilot. Seemed a little lean though.
My bike runs slightly rich at 1/4 throttle but it doesn't bother me at all, I have never fouled a plug.
I use Golden Specto at 40:1-32:1, with 93 octane pump gas.