Jesse,
One other point to make is that IMO life is all about compromises... You can't get a plane that lands slow, takes off short, goes fast, flies high, carries a lot of people, sips fuel and costs nothing..... similarly, the 24 will get your friend out of the hole better than the 26, keep the bow up better than the 26 when the wind whips up and he's trying to keep from spearing a 3 ft roller... but the 26 will have better top end than the 24 (unless the 26 is too much prop for the motor at WOT)......
I once hand-loaded some cartridges for a Remington Model 7 youth gun in 7mm-08 caliber. I thought originally that a 140 grain bullet would be best for the gun.... Come to find out, the best group I could get at 100 yds was about 3-4 inches (the barrel is paper thin and only 18.5 inches long), so barrel warp on successive shots and bullet stabilization could be problematic..... By going down to a 120 grain bullet, I was able to get 3-shot 0.5 inch groups at 100 yds and 0.9 inch groups at 200 yds with a 5-10 mph wind.... in this case the gun liked the smaller grain bullet (meaning that the smaller bullet hit the groove for that gun in terms of barrel twist rate and bullet stabilization)... translate this example to your friends' boat..... sounds like he has hit the sweet spot for take-off performance with the 24 given boat loading, power constraints and jackplate height (As mentioned by John Rrrrrrrrr)...... now the only question is whether the 24 gives him enough performance in terms of top-end speed at WOT...... if it's still an issue, then buy a Merc 2.5, do some ECU work and crank that baby up to 9k rip-ums!!!!