If the engine rpm is the same, you will have the same speed as before.
If you want more speed, get larger diameter tires.
What you have is extra HP above what is required to power all pumps at maximum.
I don't think it's any faster at top speed, but it maintains any given speed with much less effort. The original engine did not have nearly enough HP to power all of the pumps simultaneously at maximum load. I think that over the years I have read that the tram pump needs at least 12hp at maximum rated speed & pressure, the main PTO pump needs 8hp, and the auxiliary PTO needs about 3hp. That adds up to about 23hp. No problem for a 25hp engine, right?
Well, not so much. The 25hp number is a maximum gross hp rating - or to put it another way, wishful thinking. The recommended continuous net hp for the Robin EH72D (and probably most any other 750cc class small engine) is around 16-18hp, which falls pretty badly short of the real power requirements. It's close enough that we can slow down and still get the job done, but it takes a good bit of skill and patience.
So far, the new engine allows me to be a good bit less impatient.