Hi Harvy,
i used to own a a6 saloon TDI 245 sline and it was very nice indeed but a black edition would have been better for me on two points : privacy glass and Bose sound system - bling bling but hey, they just look cooler and sound better (inside)
as for the engine, I never felt like I needed more... in the real world...
having said that I now have a tdi 272 and yeah, it’s better... as for the bitdi, it must be quite something
i’ve owned various VAG car over the years , petrol, diesel, 4,5,6 cyl, turbo, non turbo: engines were NEVER a problem...
good luck