i have had mine for about 13 months now and from what i have gathered a standard 55 is adequate in all respects for a dragon. they are not overly active and tend to stay in a couple of places most of the time.
the important thing for them is the lighting and the temperature. if you can properly fill these requirements then you shouldnt have any problems with your new pet.
and btw he/she is a real cutie
and heres a link for beardies that you might find usefull
www.beautifuldragons.503xtreme.com/home.html