I would say a flat bottomed boat even at 23' will be pushed easily with 115 hp. That's not a speed demon but will get there very efficiently (easy on the pocketbook too). I believe Seaway is using a 115 hp OB on their "new" Seaway 24' DE. That's a good looking boat for around $43K.
i have a very similiar boat, samson 23 full pilothouse with a honda 225 weighing in around 6-7 k lbs. It diffently doesn't need the 225. i very rarely get over 4000 rpm. On a flat day i have opened it up and got on plane doing about 28 knots. i'm usually cruising aorund 3600-3800 at 15-17kts. If i ever need to repower i would put a 150 honda or maybe a 175 suzuki. i'd bet the 115 gives him a 11-14kts cruise. just my 2 cents