Wired on tyres, 25mm+ on rear perhaps 22+on front, anything less is
painful if you're 3+ hours in the saddle. Rider fatigue caused by
constant road shock will slow you more over a long ride, than a less
than optimum aero tyre/rim combination.
If you 'need' narrow tyres, use tubs, a 23mm tub is more comfortable
and grips better in the corners(than 25mm wired) due to a longer
contact patch at an appropriate riding pressure. Steering response
will also become less jittery with a short trail set up. Confidence
in cornering over rough surfaces improves reducing rider tension and
improves speed through corners.