Mine's a 548 War Eagle, hull weight is 353 lbs. 4 stroke 25 yamaha (2000 model-the lighter ones), short shaft. With just me, my tackle, cooler full of fish and ice, battery, 3 gal tank, and snacks, it runs right at 30 mph-I've seen 30.5 (GPS) before but more norm is 29.6-30.1.
Put the GF in there with all her junk she brings along, and lose about 2.5 mph.
With the lighter loads, I'll see 6190 RPM, max. On plane in just a shade over 3 seconds. 3.2 is the fastest I've been able to record. 3.8 the slowest. 11" Turbo hotshot prop. Idles at 795-810 RPM.
I also ran it once with a 4 stroke 15 Yamaha. It was a turd, more of a turd than it is now. On plane in about 6.5 seconds, top speed 23 mph with the stock 9" pitch aluminum prop. I think I could get 24-24.5 mph with a good stainless prop but I ended up selling the motor. I figure a 20 would've run about 25 mph tops, but it would be a slug out of the hole since it's the same motor as a 15, just a little more top rpm power.
I wished I had a 40 on mine sometimes, then other times I am GLAD it's just a little 25. That little 25 uses so little fuel that I normally have to throw out 2/3 of what is left in the tank after a day's trip anyway. But if I put a 40 on it, I pick up about 80 lbs more weight on the transom which I'm not excited about. I'm going to wait for the NEW Yamaha 25 to come out next year. If I like it, I'm buying one. I have heard some info about it and so far, if it's gonna be what they're saying it is, I'm having it-but it'll be expensive.