I buy my rear tyres from a mate who bulk buys them at ten a time.I have Mitas CO-2's which i pay 30quid a time and for green laning i have to say they are unrivalled.Not the best although they cope well,but they last ages whilst giving much better confidence on rocks than most tyres i have tried.In deep bogs they do well although you have to have some speed/momentum!! 
. Can you please let me know whereabouts you got 'em from - ta in advance. Geoff