I would have to believe that the auger could take all of it (I may be giving some overseas OEM too much credit). Most current midsize SSL and CTL's make around 20 gpm at the aux, plus or minus a little (and have since the early 2000's). That said, there is apparently no way to tell what the specs of the motor are (looking up specs that I could find, there is wide range of spec options on these auger motors). So to be safe, reducing the rpm would reduce your gpm and get you down to 15 gpm (you can put a gauge on your aux. that would tell you exactly what rpm gives you 15gpm) my guess is 50-75% would be in the ball park. However, it sounds like 15 gpm is a guess as well. Perhaps a bigger issue for you could be your psi. Your making 3300 psi which is pretty high, if there is an issue for the motor holding up, it may be due to the psi the machine puts out.
I took out the large orbital motor on my Diamond a couple years ago (hit something to big to shred). Running 38 gpm at 3500 psi and blew the seals, it did not grenade. May not be apples to apples comparison, but I don't see contamination being an issue if it failed, I see you blowing the seals out or the high psi setting snaps the shaft.
So I made an impulse buy at an auction for one of those cheapo augers from JCT.
