Someone mentioned that there will be no difference in stand over. There may be, it just won't be predictable on wheel size. Some 26s may assume bigger tires than you would run on the road, so you could loose there also, but not significantly.

I run Schwalbe marathon slicks in 1.5". There are plenty of choices, you don't want to go skinnier than that, even the racers are drifting back to fatter tires since it turns out they are fast. Maybe not 1.5, but for what touring involves even 42 mm may be an uptick.

Why wider tires offer less rolling resistance - Canadian Cycling Magazine

https://janheine.wordpress.com/2014/...nd-fast-tires/

https://janheine.wordpress.com/2014/...e-is-too-wide/