i think i can help a bit i did a road trip to le mans in a e39 535 and my parents have had a few audi's they are both very good cars.

535 v8 (245 bhp)is the much better car for driving quick and strangely better on zoom juice than a 530 (231 bhp) when driven normally. plus it growls at people when equipped with a sports exhaust
the a6 is slower (just under 200 bhp) doesnt handle as well but we had an audi 80 that went to 230,000 miles before my neighbour parked his vaux frontera on the drivers seat it had plently left too.

im hopefuly getting an MY 2000ish a4 or a6 2.5 tdi. early next year now that can haul ass and do 40+mpg