It seems that you answered your own question! The most practical difference between the 25 & 30, AFAIK, is that the 30 is available only as long-shaft, while the 25 is available as either short- or long-shaft. I needed a short-shaft motor for my boat.

I have a DF25ARS, and in another post I described changing the air intake aperture from the 25 HP part (small opening) to the 30 HP part (full opening) at a cost of $5. There is speculation that this may be the main or even only difference between the two motors. After making the change (from 25 to 30 HP), I got about a 1-MPH increase in top speed of my 250 lb 13 ft aluminum boat, from 29 to 30 MPH. Not worth $500, IMHO. If your boat is designed for a short-shaft motor, you would probably get better performance by having a 25 HP short-shaft motor on your boat than by having a 30 HP long-shaft.