I recently completed and have flown an LT-25 powered by a very old Enya .29 sleeved bearing engine having considerably less power than a modern .25 and the Enya pulls the plane very well. I can't imagine needing more power unless the dihedral is greatly reduced and the plane set up for sport flying and then I'd consider a modern .32.... no more.

The most important engine consideration in my opinion depends slightly on if the plane will be flown in an area having little wind. Without some headwind, the plane is a floater and the idle must be very low to get the plane to come down.... so an area with light winds requires a motor that will idle well.