Have run S20s on a few bikes and have been happy apart from that they wore quickly. I hear that's sorted with the S21s, but I now just run T30s on the road as I reckon it's what 500GP racer Ron Haslam uses on all his track school bikes and his ex WorldSBK son uses the same, so they should be good enough for me on the road.
All those saying about problems with RS10s on the track...That is not a specific trackday tyre....It's a fast road / track tyre.
Why would you fit that instead of the track spec R10 tyre?
The R10 is a fantastic fantastic (so good I had to say it twice) tyre. You have to keep on top of tyre temperature, but it made my old GSXR 1000 K5 corner like on rails and I expect it will be even be better on my ZX10R when I fit a pair.
The tyres need heat and I have highsided myself off the bike by falling foul of this, but this was on the K5 and I would imagine the ZX10R may save my arse with it's electronics.
The tyre is actually road legal and I have used them on the road, but again, you better make sure it's a hot day or you have a new bike with electronics.