One more thought on the 4-6-8 cylinder question. A 4 cylinder may be straining its guts out to do what would be loafing for an 8. How long do you think the 4 is going to last at that output level? The lifespan of the 4 could be quite a bit less. My 560 has over 342k miles on it. I figure three things made it last this long:
Good maintenance by the two previous owners.
Plenty of reserve power so the engine was seldom stressed.
The two previous owners didn't have near the lead foot I have.
For city driving, I vote for a stick shift diesel!