If you order the pulley from Flat6, the price includes for a new belt.
The belt supplied with mine is Gates part #KO60806. Its smaller than the original and a tight fit, but being Gates its of good quality.
As an aside, I fitted the new Flat6 pulley last week and it took me about 2.5 hours from start to finish - but that's because I used a junior hacksaw (not a dremmel)& a file to remove the exposed alloy lug. Doing it a second time I could halve the hours....
As for my experience with the upgrade, definately an improvement, noticeably in the 2,000 - 4,000 rpm where I do most of my driving. The pickup improvement from the lower revs reminds me of a car thats just had its major service - a nice, clean, linear pull.
I checked the voltage at the battery terminals and the "before and after installation" voltage difference is not worth considering above 1000 rpm.
But even more suprising is that the improved cabin noise (obviously with the roof up), its much quieter, with less engine auxilliary noise coming through the bulkhead.
Coupled with the low temperature thermostat I fitted last year, both have been well spent $$$ for me - couldn't be happier