well, when i say it isn't economic, it really isn't here the economic that we had here in Brasil was the 2.0 CD with Monza's engine it used to do 9 km/liter IIRC, and and it keep going down with 3.0(6 cilinder straight , as you mentioned, the german) and hits the bottom with 4.1
Here in Brasil, almost all Opel Cars are re-relesed as chevrolet.
btw, in last April i had the oportunity to drive an 4.1 CD 1995(i think) powered up with that powertech lotus, the beast is awesome i drived from here, Brasilia to a 200km city away from here, Goiania, thank god there were no radars to fine me, the car responds imediatelly, better than anything i've ever drive.