Just for comparison, I looked up the GPS tracks for my recent charter of a Sunsail 38 (essentially a Jenneau Sun Odyssey 379). I was sailing under conditions similar to Minnewaska. We took in a reef before leaving the dock on day 1, and never let it out the whole week. We sailed with full genoa, although it appeared to be about a 110, so calling it a genoa is a bit "gen-erous"
On the open stretch from East End St. John, heading toward the Bight, I was doing 6-7.2 kt. Prior to that I was only doing 4.5-5 kt along the northeast shore of St. John, but I was pinching severely to avoid having to tack. (The chartplotter says we were 60m from the rocks at East End
, although that's probably more precision than the chart can offer.)
Next day, on a beam reach between Peter Island and Road Harbour, I was doing 6.5-7.5 kt, and touched 8 kt a couple of times.
All these chartplotter numbers agree with my recollection of the SOG gauges from the boat's built-in GPS system.
This was my first time pulling a dinghy, and it did not even dawn on me that it would slow us down. The dinghy probably explains why I could only get 5 kt when motoring. But since the dinghy does not affect your hull speed, if you have enough wind, sail area, and proper trim, I would think you should have plenty of power to reach hull speed even with a dinghy in tow.