Fat Tire Bike versus Road Bike
Super hard to measure without a power meter. But you could approximate it using various web resources.

https://www.bicyclerollingresistance.com/ lists the best fatbike tyre as a "Schwalbe Jumbo Jim Liteskin PaceStar" with 36.9 W of rolling resistance.  The best road tyre is a tubular at 7.7W with most clinchers (ie normal tyres) under 20W per wheel and averaging 15W.

http://bikecalculator.com/ doesn't know about tyres specificially, but if you put 200W in and compare that with ~15W per wheel for a road bike and 36.9W per wheel for a fat bike, then you're effectively comparing 170W on a road bike with 130W on a fatbike.

Assumptions - 100 kilo rider (dressed)

170W on a 15 kilo road bike with hands on hoods, clinchers, over 10km will take 20.8 minutes for a flat road or 122 minutes up a 10% grade

130W on a 18 kilo MTB bike with hands on bartops, clinchers, over 10km will take 24.3 minutes for a flat road or 164 minutes up a 10% grade.  I feel a fatbike would be even slower than a MTB.

This is excluding the aero differences between bikes too.