[Fr. Frank]

Denny hit it pretty well.
The lateral instability inherent in a deep-V hull with no flat planing surfaces is most noticeable in smooth water. Choppy water will actually give you a more stable ride. The hull rises up and tries to ride on what is effectually two points of contact: the keel line of the v-hull and the point mid-way between the two propellers which is the effective point of thrust.
Here's a couple of notes you may already know:
a) Having outward rotation on twins helps with stability and steering, but creates a bit more drag.
b) You want approximately 3/4" - 1" of toe-in for each 24" of separation of your motors.
c) Deploying your trim tabs slightly as speed increases creates two additional small points of stabilizing drag that actually reduce your speed only negligibly and stop/reduce oscillation noticeably.

As I said in an earlier post, I sold a 23' SeaVette back in '83 that the customer took to Frank Brown for rigging with twin 300hp 3.4L Mercs. It reportedly could hit 77 mph after tweaking.

Back in 1984/85, my own 23' Savage with twin Mercury 225's could hit 57-58 mph with the bimini down.