Hi Nick,

On a 26" with 100mm cranks, for each rotation your foot moves ~628mm (or 24.7 inches), and the wheel moves 81.7 inches.

On a 29" with 150mm cranks, for each rotation your foot moves ~942mm (or 37 inches), and the wheel moves 91.1 inches.

It’s already fairly clear which will be faster, but just for the sake of it I’ll keep going. There’s probably better ways of doing this, but my brain is dead and I can’t think of them so I’ll do it the slightly longer way

The least common multiple of 25 (rounded from 24.7) and 37 is 925. Multiplying the revolution distance by these same numbers, we find that:

On the 26", for every 925 inches your foot travels, the wheel travels 3022.9 inches, or roughly 252 feet.

On the 29", for every 925 inches your foot travels, the wheel travels 2277.5 inches, or roughly 190 feet.

And so, as @Duff said, the 26" is faster “all other things being equal,” because the same pedaling will make it go just under 150% of the distance of the 29" (if my calculations are correct).

Hopefully that helps!