Your problem is the availability of all season tyres in that size. The best are Michelin's new Cross Climate and the forthcoming Nokian Weatherproof. Previous best was Goodyear Vector 4 Seasons but not available as 275/40 R20. You might get Vredestein Quatracs that size or Bridgestone A001. The Germans tend to go for summer tyres for summer, and cold weather tyres for winter, which explains the lack of availability of high performance all weather tyres. I would not run cold weather 275/40 R20s all year round.