I've got some Vittoria Corsa N.EXT in 34mm and they seem good so far. Grippy, not slow, and measure up as advertised on 20mm internal rims. Went on and inflated easily too - no levers needed! Probably not as tough as the Pirellis but no problems yet, and they should be a fair bit quicker-rolling.
What is the equivalent to a GP 4 Seasons that comes in a 38 (or 35 maybe) and works well as tubeless?