selectedBOUNDS [0.7a] [2.79]

is it possible to have “selected bounds” on while “selection outline” is off, might be a performance improvement since the drawing of the selection outline has big impact in the viewport’s performance…

Yes, outline selected can be toggled off while selected bounds can be left on, I don’t think that selected bounds performs better then outline selected, at least not when displaying it on a bunch of objects.