Just got back from America's Tire with a new set of Pirelli P7 AS Plus 3 in 255/45/19. There happened to be an applicable $70 promo, plus the 5% discount for using their 0% financing, which brought the grand total out-the-door to $1299.17, including the tire protection certificates. The P7 AS Plus 3 has a 70K-mile treadwear warranty but I doubt I'll see that. Hopefully they'll get close to 50K miles. We will see...
I only drove 17 miles so far and need more time to evaluate ride quality. At slow speed out of the parking lot the tires felt softer and more comfortable, but once up to speed they didn't seem to smooth out bumps any better than the OEM tire. More immediately noticeable though is the improved turn-in and grip. Even on fresh tires there was less delay during lane changes compared to the OEM tire. Also, there's this particular intersection near home that the OEM ProContact RX always understeers through on left turns. With the new Pirellis there wasn't any understeer and I was able to maintain a smoother arc through the intersection.
I am still curious to see if the ride quality will improve. It certainly isn't any worse than the OEM tire, but I expected a cushier ride based on past experience with the P7 AS Plus 1. However the P7 AS Plus 1 on the Model S had a load rating of only 98 versus 104 required for the Model Y, so maybe that has something to do with it.
And of course, the efficiency question! After 21,666 miles on the OEM ProContact RX we averaged 256 Wh/m. With only 17 miles on the P7 AS Plus 3 the tires averaged 279 Wh/m so far, so about a 9% penalty. However, the P7 are still very new and the OEM tires averaged 289 Wh/m the first four days of ownership last year (after ~185 miles). We drive an average of 60 miles a day and will break-in the tires real quick and report back soon with more efficiency numbers.