A few things could easily account for this (or a combo of several)
1) The beam and weight is a little higher on the 25 vs the 23.
2) the props might not be correct or properly matched or damaged. You would be amazed how much you can loose just by having a slightly out of pitch blade...when this happens the blades tend to work against one another instead of producing uniform thrust together.
3) the bottoms are different, the SC has a
slightly less efficient in a chop but a much softer ride. (personally as someone who had a career in marine hydrodynamics I love the longitudinal stepped V hull which offers amazing benifits..
SEACRAFT Boats )
4) Bottom condition
My 23 sc had twin 150's it would hit 50 wot. ( I rarely could find water where I could run like that, it was a white knuckle ride) When I went to a single 225 4stroke, it hit 40 wot on a good day. Fuel econ was much better! I went for a test drive on a used 23 that had
twin 225 2 strokes and it was scary, I thought it was a death trap. When it hit 60 the boat was so squirly it was IMO out of control and not safe. I backed off the deal. All that said, the boat handles better with twin motors there is a stability created with twins that you cant get with a singles but you have to pay for it with fuel and service costs.
Honestly, with fuel $ the way it is...get a single 4stroke 250 and cruise at 28 knots and don't push it and you will be happy.
Look at those photos above...It is calm and they can't keep the boat in the water! If you ran like that for an hour you would be exhausted (and broke).