since NiMhs do not develop memory & i see no need to discharge them at 20A or even 30A
because discharging them at such high amperes will only do one thing, heat them up..and as you all know heat is batteries no.1 enemy
the batts would have already heated up a lot when your racing your car, to further cook it in a 20A/30A discharger will only shorten it's useful lifespan.
my 2 ringgit