My arguement has always been that coral cats need more room than larger epaulettes. Coral cats actually swim about, almost like pelaegic species...during the day they stay hidden in the rock work but at night, they glide around the tank in search of food.
The space you have now is great in my opinion (others will disagree); just make sure you go overkill on the filtration (huge skimmer and UV sterilizer, big sump and trickle filter), and keep rockwork limited to decent hides; ensure there are clear glide paths across the length of the tank.
If you are still concerned about size you couldo with a papauan epaulette, h. hallstromi. They max out at around 27". The drawback is they seem to remain hidden most of the time...mine only comes out of the rockwork during feeding, and late at night.
If you want to see a grown eppie, swing up to jay's...he has an adult female in the 300 gallon register tank.