No direct experience, but just got off the grand canyon and SUP'd as much of it as I could be away from the oars on my raft (so most everything up through GC 4-5) on the NRS earl- NRS Big Earl SUP Board at NRSweb.com
and some on the NRS baron- NRS Big Baron SUP Board at NRSweb.com
The smaller, thicker earl seemed better in almost every way. The larger baron felt like a picnic table, wasn't as stiff, didn't turn well, was harder to lean for eddy turns and diagonals, and surfed much worse.
So if you want something just stable for flat or low-performance, the saturn size/design looks fine, but if you plan on any level of performance in wh20, I think you want something shorter/narrower and thick/stiff.
This isn't bashing saturn at all, I've had a saturn raft for 4 years now and it's been great.
fyi, GC is awesome SUPing, although staying on your feet through the big waves and holes takes some time, and brown water makes catching the fin in shallow areas pretty sketchy.