Recommended is a much different standard than
required.
Just how much "reduced performance" is the question Numbers aside it's inconsequential in normal driving of our trucks. Performance cars (or pseudo performance cars) will feel the difference. That 350 Mustang will still get to the next stop light sooner. Heck my S2000 will.
This is what Colonel Cooper referred to PII. Preoccupation with inconsequential increments.
23 gallons is my normal fill up. At 60¢/gallon extra for "premium" that computes to nearly two six-packs of a good micro-brew to put it in a meaningful number. I'll drink the beer until I need some increased power.
-- Chuck