Another data point:
I received my renewal passport just 14 days after I mailed the renewal application via regular mail (70 cents postage), with standard processing. Mailed from upstate New York to Irving, Texas, on August 11; my check for the processing fee was paid by my bank on August 16; new passport was issued on August 22, and mailed via Priority Mail from Hot Springs National Park, Arkansas, on August 23; received new passport today (August 25).
Kudos to the USPS and the Passport Office!