If you're looking for cheap horsepower, the Nice ain't it. 123cc is the limit of "cheap" displacement and even that's a one-and-done. If the cylinder ever needs another overbore, time to either re-sleeve, or replace. 127 is more solid...and a lot more bucks; the machinework required is a world apart from any 49cc-based or Chinese mid/big block tunes. Decent used cores are few & far between. The reasons for sourcing a Nice are mainly qualitative... refinement & reliablity, as good as it gets. The only quantitative advantage is longterm cost-per-mile. After 22,730 miles, the motor in my daily rider is still healthy & smooth as ever. Without a substantial headwind, the bike will consistently hit 63-65mph. I've run WOT for 20-30 miles at a stretch, many times over the years...not exactly "babying" it. The rearview mirror is usable at any speed and the prototype Super Stealth pipe is intact after 18,000+ miles.
Make no mistake, a stock-headed 123-127 tune (beyond this level, the bucks multiply) can reach 70mph+. That represents a 30-40% power increase, over stock. But, those additional 5-7mph will be seen on the speedo, more than felt on the seat-of-the-pants dyno. Below 50-55mph, there's not enough added torque to make a substantial difference. It comes down to how many bucks and miles of service life you're willing to exchange for another ~5mph.
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