Yeah, my ol' man bought one in '07 - the 400. First thing I said was his engine looked exactly like the one in my old DRZ400S. Upon closer inspection I realized it was indeed built by the same company.
His tank is about 5 gallons on that 400. I've got an 800, and my tank is nearly HALF that! About 2.5 gallons. I piss through fuel like crazy. She's a thirsty bitch!
40 to 50 miles is about all I'm good for on a long trail ride. Could probably get more if I kept my thumb out of the throttle .... but if I wanted to do that I would've bought a 250.