Tall slicks

Ball park 10 % for slippage.
Your results may vary , but this comes close in most cases.
The shorter tire takes less energy to get moving since it will weigh less and the weight will be closer to the axle center line........miniscule difference , but it is there.
You know the math , so figure which ratio works for the taller hide if you want to keep them.
You will have a ton more choices for gears with the 9" , so this opens up a lot of possibilities.
Slicks come in a lot of different diameters too , so maybe a 30" tall ?