I think people and I said it before as well, mean tuning the stock clutch involves actually changing the fly weights, primary/secondary springs, helix ... on your machine, test, change and retest until satisfied.
I believe this does give a better result then buying a preset clutch kit from one of the venders. There are many variables and the venders have to compromise. If you do it yourself or work with someone that is doing it you can get exactly what you want.
This is take a lot of time, a lot of data collection and maybe a lot more money then a kit will cost you, but it will make a difference.
I spent less than a clutch kit on mine and I don't think that the performance could be better. I got advice from people that had experience, took my time and collected pages of data. I also know people that race rzr's and they let me use their old kits and kits that didn't work for them to mix and match until I found what worked for me.
My clutch engages at 2,000-2,100 and goes right to 6,020 -6040 rpm from a stop and stays there until it fully shifts out then climbs to the rev limiter. 63 mph at 6,300 rpm showing on the tach/speedo. No engine mods or controllers. This is a stock 08 and I can out drag any of my friends RZRs and RZR-S with their pipes, clutch kits and fuel controllers. The power is in the clutch tuning not bolt on parts.
Don't ask what parts I used. I'm racing it and don't want others to know the secret. Only 2 people know, we discussed some things so I kept them up to date.