Two sets of wheels for mine. 700x40 knobby and 700x30 slick.
It's a barely perceptible change in gearing.
I don't have a power meter.
My road bike, at 700x25 with a 34/30 granny gear feels about the same up a steep hill as my gravel with a 40/42 granny. Don't forget the rowdy bike is 4lbs heavier.
I have two rides near by. Gravel that climbs 3100' in the first 13 miles. And a road ride that happens to be exactly the same amount of climbing. Both hurt. In terms of effort, the gravel is harder and much slower. Just thought I'd throw that in for the the guy who thought 1000' in 6 is a big climb.
In the days of 8-9 speed, everyone had multiple cassettes. Sometimes you want to spin, sometimes it's steep. With 10/11/12+ this is less necessary. If you are riding around with a cassette that isn't optimized for your legs/terrain/ and wheels. Do it right away. It's literally the first thing to do to ensure you're riding as well as possible.
Road, 12-25 flat days, 13/29 low end for trailer, 12-30 for mountains.
Gravel 12-36 rolling terrain without much steep. 11-42, getting rowdy.