If you are looking at the Astro 40 motor, at 12V that motor will be giving you just under 8000 RPM's if I read the specs currectly. At about $100.00 that is a lot more than I would be willing to pay.
Unless you want that boat to stand up out of the water when you hit the throttle you do not need that rapid torque to get up to 8000 RPM's. The Pittman motors that I ran in FNS Mogador were 24V rated motors that were run on 12V. This produced 5600 RPM on the bench, and I estimated about 4400 RPM's in the water. At flank speed this would allow this 6' 3" boat to cover 100' in 30 sec's. Not as fast as what you would like, but you can obtain a Pittman 14V and run this on 12V and you will be pulling close to 10,000 RPM's.
The E Bay item # 3180386441 is the type of Pittman motor that we often run in our warships.
If you can find one of the silver cannister Maxon motors rated at 7.6V , these can be over run at 12V to give you near 10,000 RPM.
The Astro 40 is a great motor, and is very efficient, but you can find motors out there that will do what it does, draw more amps, but cost a lot less.