heres what i think........
if you are dead set on getting a clown fish, try and give it the best available habitat that you can give it and still be healthy....
for a 6 gallon tank, I would recommend that if you HAVE to get a clown fish, get one that is extremley young, and plan on keeping it until it grows to a medium size.... as long as you stay on top of water changes and there is enough room for the animal to swim, you should OK. Notice i say OK, as many people disagree with me on even giving a clown in a 6 gallon a shot. Do what you think is proper in the situation, and you'll be alright....
5 years ago, no one would have even thought of keeping a saltwater tank in anything smaller than 55 gallons, and look at us now (.5 gallon pico tanks!!!!!!!)
nano reefing is awesome, as long as you are responsible enough to handle the challenge!