The following printers are built around the same interchangeable set of parts.
The T650n is the entry level network laser printer built around the 4062 machine
The T650dn adds a detachable duplex unit for double sided printing.
The T652dn adds a 550 sheet paper input tray and the duplexing unit is now integrated.
The T654dn adds an increased printing speed.
The T656dne adds a touch screen.
The X651de adds a multifunction document scanner / copier. The X65x range is built around the 7462 machine but the parts appear to be interchangeable with the 4062 machine.
The X652de adds a fax function
The X654de adds an increased printing speed.
The X656dte adds a detachable second paper tray and an 80GB hard disk.
The X658dfe, X658dme, X658dtfe, X658dtme integrate a larger output tray with offset stacker and stapler.