Always train harder and long than you have too It pays off, I run 20 +2 formats at Crow and Battlesburg all the time, actually its my usual and its no big deal Just ride smooth and not stupid and pace yourself and its no biggy, plus you will be used to that and the Malvern 4 lap races are like 4 sprint laps no problem. Plus it benefits me because i started racing double class so it helps alot
I could see the 20+2 being good for building a cardio base, But James has the right idea for actual race practice