I'm replacing a totaled '99 Avant.. I'm down to selecting between a '04 A6 w/4.2L or an '06 Avant.. there's a 10k difference - any advice on how the engine performance compares, does the '06 3.2 compete w/the older 4.2l?

The older 4.2 is a better performer than the 3.2. But the C6 is a far superior car to the C5. I would take the C6 with the 3.2. BTW I drive a C6 with the 4.2.

thanks, very helpful... this may get me kicked out of the forums but what is the C6 vs. C5 designations? Is that the different model types e.g. is C6 the model type that was introduced in '05?

Yep, C4 '94-'97, C5 '97-'04, C6 '05-present

And I would get the C6 if I had the choice.

I agree. Go with the C6 (newer Frame). This link explains it further. http://en.wikipedia.org/wiki/Audi_A6

No NO!! Buy the older one and send me half the difference.

I'm noticing a recurring theme throughout this forum, that is the 3.2 V-6 doesn't seem to get much respect. No real badmouthing, but always mentioned as a distant second to the other currently available engines (2.7; 4.2). I understand the mod crowd preferring the turbos, but is the 4.2 that much better than the 3.2? Just curious.

And yeah I've got the 3.2

I have the 4.2 and do believe that it is significantly better than the 3.2. Not just the engine, which has far greater power (80+ hp), but the 4.2 comes with a larger number of amenities as standard equipment.

Fair enough- by amenities I guess you mean items related to the chassis and operational systems of the car, and not the engine itself. As far as the horsepower goes, I've never felt at a loss for power with the 3.2, and believe the mileage is somewhat better as well. At this stage of the game, I'm more interested in the mileage figures. Oh well.
By the way, I've also seen it mentioned that the 4.2 has awider stance, or something to that effect. Is the body or the chassis somehow different on the 4.2 from the 3.2??

The C5 4.2 A6 has larger and wider fender wells. A "wide body" is what's it's generally referred too as. The C6 (2005 and beyond) vehicle bodies are the same. There are no turbos for the C6. 2004 was their last last year. Only the 3.2 or the 4.2 are availiable for the C5 A6. Their is a V-10 but it's in the S6.