Another Mitchell Overdrive question - 26% or 36%?

[SDJason]

Hi all,

Long story short - I'm planning to have a Mitchell Overdrive installed.
I have a 1930 Town Sedan, with a Snyder's 5.5 HC head and 3.78:1 rear end.

The local Model A folks who will be installing this recommended I get the 36% OD. From reading various threads here, it looks like 26% is what most folks get and recommend.

So - just want to pick the collective brains here: why should or shouldn't I get a 36% overdrive vs. a 26%?

Thanks!