After searching,I saw a PT boat on a leasurely stroll

Note that a 900 motor is almost like a 700 with a gear reduction.You can stick a big prop on the 900 and it will grip the water and shift a displacement hull,not dig a big hole to the rear of the transom.
If you were to put large props on the 700bb and can't get it skimming with motors turning at several thousand rpm then the motors,escs and battery will be effed.

I think your 900 motors are a better fit for your cruiser and you could increase on the props until the revs fall to half the free running figure.Perhaps even up the voltage and watercool them.

Tony