Flats tend to have more tension, so going one step down in gauge will probably be pretty close, depending on the strings.
As an example, I recently went from a set of DR Nickel Lo-Riders .105 .85 .65 .45 to a set of D'Addario Chrome flats .100 .80 .65 .45 and still had to tighten the truss rod a little.
__________________
"If you don't feel it, don't play it." - J. Jamerson
High tension sucks. So I've been told by a number of my clients. Medium tension on the other hand is likely to offend nobody or everyone. Let's hear from the medium tension fans.