10.5 knots !?!?....LOL Not my little boat brother. I can probably hit 7 or so with outgoing tide I'm guessing but not 10. I was fighting it at 3 knots and rough chop for a long time my first trip out. Hopefully this time will be easier with somone more experienced than myself leading the group. I'm excited and looking foreward to it.
10 knots over the ground - NOT the water LOL. I did it in a 25ft boat my first trip (including sailing all the way around Long Island) as well as 2 trips to Block in my 32' Morgan which is a heavy slow cruiser that usually cruises at 5.8-6knots. If you time the tides so that your boat is going through the Race at peak tide, the current can move at over 4-5knts - add your 6 knots of boat speed and you have 10-11knots over the ground showing on your GPS.
Now you won't be doing 10knots the whole way or even close to it but if you really time it right - which I try to do each year then you can use the tide so much to your advantage. Pick up an Eldridge - it shows current diagrams of the entire Sound showing how fast and where the current is for every hour of the Ebb or Flood.
For example 2 years ago we left Mt. Sinai for Mattituck at 4pm Fri afternoon and did 5.8 knots over the water but 7.5 knots over the ground the whole way to Mattituck inlet making the first leg much quicker. Now in order to make the MOST advantage for the Ebb (all the water in the Sound flowing back out through the Race and into the Ocean) we left at 3:30AM in pitch black the next morning just before slack tide. For the first 45minutes to an hour our boat speed was the same as our speed over ground 5.8 knots but after that hour when the current picked up (and at the eastern end of the Sound it is much stronger than the western part) we were doing 7.5 knots then once we got around Orient Point picked up to 8 - then once we were North of Plum Island 8.5 then 10.5 through the Race (where the tides and currents converge) then 8.5-7.5 for the next hour after the Race with a straight shot to Block. Then once you are out in Block Island Sound the Ebb is most likely ending (6hours) and the current will reverse but at this point if timed right you are past it and shouldn't hit any negative current slowing you down.
So anyway sorry for the long post but was just trying to illustrate how a little bit of planning by using Eldridge and leaving at the right time can make our slow little boats into speed machines for 6-7 hours per day. Where the opposite if you left at the wrong time instead of doing 7-8knots you will only be doing 3knots like you described - over a 6 hour period that is the difference of 30 miles!
I would be more than happy to help plan out the trip though or even go through Eldridge with you for next year. Regardless though I think if we get a lot of boats for this trip we could leave at anytime day or night and still have a lot of fun as there is no right or wrong way in reality.