I think standover height is one of the least important dimensions, although if you forget, hop off the saddle, and smash your family jewels, it will probably be very important.

You want to be comfortable on a tourer. Small things can become big when you're riding all day, day after day after day. You can tweak fit by raising or lowering the seatpost, sliding the saddle forward or backward (and changing the tilt) and swapping the stem for something that does what you want.

Don't ignore the reach to the bars. If you're too stretched out you won't be comfortable.

When you're buying a new bike you should get exactly what you want, fit-wise. When you get a reallly good deal used you can do fine on a bike that isn't exactly right but is close. Keep tweaking the fit and enjoy the ride!