I currently have a 10 gallon with a 24" 4x T5HO and they are working fine in my 10 and I think they would work fine in the 55 also, but I really like LED's (who doesn't like that shimmery look) and I am upgrading to a custom acrylic 55 gallon tank that is actually two sections with tubes connecting them in the middle. Each section is 22"W x 24"H. What light would support coral but not kill my wallet (trying to be under 150~200 since I have to buy 2, one for each section).
Here's a picture of the tank:
http://imgur.com/uHe1WFH
Here's a picture of the tank:
http://imgur.com/uHe1WFH