Well, we're in the same boat for what we want, I do also race in stock, and want to keep a reasonably budget, thus I like to have a reasonably battery life time.
So far, I've been discharging mainly in the car, since most of the time I'm practising, and race the batts till they drop. In this situation, there's little (maybe no) need for an 20 amp discharger over a 10 amp ditto.
If you go a lot to regular races, where you only race for 5 minutes, there might be a need for 20 amps discharging.
I think the big question is: shold it be an equalizer with auto cut off (which usually is low amp) or shold the cells be discharged down to zero volt?
In the last case, it's a straight forward: Get a high amp/zero volt tray, to complement your Ice.
Personally, I've been using a 1 amp, 0,8 volt auto cut off equalizer so far. To be on the safe side. And with good results. Both on the track and on the discharger. After approx. 30 runs, I still get ery good data (almost as good, as when the pack was new) But I'm more and more considering getting a 20 amp tray and go down to zero volt for even lower IR and higher voltage. It seems like the GP3300 wont be hurt by doing this. But I dont got personal experience.
Someone else please chime in