Re: More?'s is a 90 fast enough (new glastron)
One other comment. I have a 15 1/2 foot Cheetah bass boat with a 93 Yamaha 115 and absolutely love the engine. The holeshot is great, it's just a sweet running ride. Best engine by far I've ever owned and picked up the rig for $2800 to make it even sweeter. But, it's primarily a fishing rig, and occasional recreation. Yeah, I know, it'd be better if I had a real fish-and-ski, but then I wouldn't have this sweet Yamaha 115.
That said, if your kids want to do some real wakeboarding, and you're going for more of a ski boat, have you considered getting a real wakeboarding boat? That would be something like a (used?) Mastercraft, Ski Nautique, Malibu, etc? Sorry guys, I still prefer inboards as far as reliability and ability for the backyard mechanic to work on them, and they are the boat of choice for true wakeboarders. If you are like me with little marine experience but adequate automotive skills, that car-engine-in-a-boat is something I'm partial too, plus there's ton of more torque when you add those weight sacks to the back of your boat to provide that huge wake for your kids to jump.

I'm almost 40, but bought a wakeboard about 10 years ago but have always tried to wakeboard behind fish and skis, and it stinks! There's no wake! You can't jump if there's nothing to jump!
Alright, that said, you could always get a Malibu wedge installed on your ski boat transom that essentially plows the water to provide a nice wake too. Not sure if that's as good or comparable to wakeboarding boats though, but if you're thinking about spending $20,000 on a boat, that much money would get you a really nice used I/O with a 350/351 cu in engine with torque to boot. --Steve