We're a small structural engineering firm looking for advice on getting either an older HP 650C from a another engineering firm relatively inexpensively vs buying a new HP 510. Currently we run an old version of AutoCAD but that will be changing soon, and our plotting needs are limited. My concern is that the 650 will be obsolete and I'll be buying a new plotter anyway. Does the 510 do anything the 650 can't? Thanks, smb