Without modding the hull, about 40-45 Km/h, maybe a bit more.
The stock hull comes with molded in "breaks", at the rear part of the sponsons, these need to be filled and flattened so the hull runs more free.
I've seen Key West doing an astonishing 80Km/h+, but the hull was glasscloth/epoxy re-inforced, the rudder offset and very shallow (low drag) and it had a brushless motor and modded prop...
Just the shape was original, sort off, even the hatch was modified to be really waterproof.

Regards, Jan.

P.S.: why bother with an outdated design, when there are so many epoxy hulls available, that will run much faster...