I think that the main differences are a few cosmetics and also the S's as far as i know came with the bigger front calipers and rotors. Have a look at your front brake calipers they should be finned and i think they are alloy not 100% on that. They front brakes should be the same as the V8's.
What's the difference between understeer and oversteer? Understeer is when the driver is scared. Oversteer is when the passenger is scared.
The factory standard suspension used on the VN execudores sits 1" higher than the FE2 suspension used on the S-pack commodores, coming with the FE2 suspension are high performance calipers (they have cooling fins on them and that's it) on the front.
For some strange reason (known only to holden) the S-pack has less torque than the execudore, and it weighs more, so off the line acceleration is slightly poorer. Mechanically they should be identical, in the days of the VN having the 's' badge on the car just meant that it had a different suspension and a few more bits and pieces inside. That's it really. It doesn't go any harder than the exec.
Bite off more than you can chew, and chew like hell - Peter Brock (1945-2006)