needles

The result is about a 1% change in speed and the tire is lower profile...

There are a ton more winter options for 255 than 265 is the reason I am asking.

derfA8L

I think you'd be alright. As for winter (snow) tire performance, you are actually better off with a narrower tire footprint---255 vs. 265. IIRC, Audi's winter tire package is a 235 width on 19" wheels...same 19" wheels that originally wore 255 width tires on the 2008 & 2009 D3 A8. Based on that, I gotta think that going down from 265 to 255 on the 20" wheels should be fine. Tire Rack, or a similar vendor should be able to give you the definitive answer.

needles

I said screw it and got a set of four used Dunlop Winter Sport 3D from eBay (265/40R20). 8-9/10 tread and only 1200 miles on them. Cost HALF of a new set with free shipping. $15 per tire to install at a local shop.

We had snow and ice this week and I had been putting off the winter tires, but those Pirelli P-zero summer performance tires were terrible.

derfA8L

And those should be fine as well 😊