Ok, finally got around to measuring. The front to rear depth is 16". The base is smaller. I understand Mitsibishi has a DLP rear projector at 57" that is only 14" deep.
By the way, if you go plasma, check the rated half-life of the display out. It is rated in hours and is the manufacturer's approximated time where the colors reach hafl the saturation levels from when it is new.
I know Pioneer Elite's are rated at 60,000 hours. Panasonic rates some of thier models up to 100,000 hours. The trade-offs is the brightness. Pioneer tends to be brighter than Panasonic, thus the shorter half-life. Again, do not trust what you see is a store demo. A properly calibrated set is not going to look anything like the demo units in a store once at your home.
DLP's, using color wheels, are all rated at lower black levels than rear projector LCD/LCOS sets are. They also suffer lower ANSI contrast levels. I have not read a review of some of the new DLP sets that use three DLP chips instead of the color wheel. That is not to say you cannot find LCD/LCOS sets that are worse.
My reference point always leans towards the higher end model sets. Honestly, the lower end sets, of any type of technology, hold no interest at all for me.