Hi, I owned a 1999 P IV w/a 200 Opti (2.5l ) for 9 yrs. and I now own a 2008 P IV w/a 200 Opti (3.0 l). I guess that the first thing that comes to mind would be the hole shot. The P IVs hole shot is very impressive w/a 25 Trophy and will flat knock your socks off with a Fury! I think that there would be no comparison to the hole shot of a P III.The layout is great, and the net holder is something youll wonder how you lived without. I do miss the day box on the P III,, but I guess on the P IV its just a lot bigger. Top end may drop 1-2 mph depending on load. Rough water ride is as good if not better than the P III. Although, I havent been in a lot of rough water since Ive owned the P IV. All in all I would say that you would be pleased with the move. Im sure others will come on with their opinions. I hope this helps!good fishing,john