OP, we have a FG XR6 with Lux pack now in the family and it's a very nice place to be. I'd say the FG2/FGX G6E would be an even nicer place, would make a very comfortable town & country car. They are mechanically simple, and should last 3-400,000km.
Honourable mentions: BF V8 Fairlane: with 5.4 SOHC V8 and 6 speed ZF, they will spin at 1100 revs at 110km/h on the highway - that's cruising torque! Finding the V8 Ghia that's not a G8 with stiffer suspension is the harder task.
The final Holden Statesmen have acres of rear seat room, overall just a big luxo barge.
I have a soft spot for NL and AU (NU??) Ghias and LTDs...