I would advise against getting a fish that will ever outgrow your tank. Even moreso than what I thought, I find the most amusing thing about any of my fishtanks, be them marine or freshwater, is watching a fish I got from "youth" grow and develop into a full grown fish.
It's just no fun to train a puppy and housebreak it only to trade it away once it starts to behave and attach to your family.
Granted, we're dealing with fish and not puppies - but I would consider sticking with smaller fish.
I was in the same boat you were, I was thinking about starting an aggressive setup - but when I sat back and looked at it, it just wasn't a good idea. I bought a retrofit kit of 2 X 96W Power Compact lights and started a 30g reef. It's finally starting to look like a "reef" at almost 3 months and I love it. I have 2 percula clowns, a purple firefish, and a 6-line wrasse. All 4 have great personalities and are hardy fish.
My $.02
