I believe the engines are 6,500 hp each for a total of 13,000 hp. 615 hp or 650 hp each would not do much to move the Mount.
As far as top speed, remember this is a full displacement vessel so the length of the ship determines the top speed as long as the hp is adequate. I doubt it could get out of the hole and up on plane even with the 13,000 hp.
Their web site appears to be down at present, but I think my memory is somewhat accurate.
R2B