Size matters less than bio-load and what you are trying to do.
I like my simple "berlin-style" reef.
I would recommend it on any tank with a heavy bio-load because otherwise you end up with a layer of skum on the top of your tank. Its inevitable in my mind/experince.
The good news is that if you just want a simple system (like the "berlin" that I have) all you need for filtration is a skimmer.