I wouldn't be surprised if it could top 40, or maybe even 50, knots. Likely twist herself up into a knot before she ran out of power and 4 20+ foot diameter screws can move a LOT of water.

Not sure I'd hang my hat on the old hull speed formula being the limiting factor either. You can increase maximum hull speed with modified bow shapes.

“Life is life and fun is fun, but it's all so quiet when the goldfish die.”