The S20 Evo has a different compound and lasts longer than the S20. Went to Lemans last year and S20 was flat spotted on return. Done Assen this year and the rear is more rounded. Bridgestone say S20 Evo should last about 20% longer than normal S20. Think price diff is only a few quid too.
I have just put on S20 evo got 1900 miles from the S20 however might have to get shot of blade as same paint scheme now on a cbr300 as in last weeks MCN gutted .