We had a 1999 RM125, with SST pipe/silencer... stock reeds if I recall and the 144 kit.
The bike when we finally got it jetted somewhat close, was very fast. Much faster than any 125 I've ever ridden and I've ridden some of the factory 125s.
Here is the scoop though - it was super finicky about jetting. That thing would change by the hour it seemed. It was also a nightmare to get jetted right - I wish I could remember what the jetting was on that bike.
If you get the 2000 kit, let me know. I'm considering sending a 2000 RM125 cylinder & cases (so they can be relieved a small amount) to Eric. If I get mine done and jetted, I'll let you know what baseline specs I came up with for my altitude and temp.
Mikeee P