Jasper, I recently sold my Gasser EC300 enduro bike. Awesome power buyt also easy to trail ride. Smooth 4 stroke torque for tootling along, evil power when you drop it a gear and tap the clutch. It truly was a backwheel beast when opened up.
Gas gas also make a 2 stroke quad with the same engine in. Parts are cheap enough too for them. I paid £90 for a piston, rings and gasket set with a little end bearing for mine. Being a 300 the piston doesn't need changing as often as say a 125 or 200 as it doesn't get 'caned' as hard.