Windage with our current hardtop (or with the hardtop on our previous boat) is a minor detail. We don't notice any additional impact, given existing windage on the hull/saloon/flying bridge (now) and the hull/bridge deck (before).
And since the hardtop is structural, we have stuff mounted up there, don't have to worry much about snow loads this time of year, it gives us a better mounting situation for the bridge enclosure, etc.
OTOH, we do experience slightly more windage when the full bridge enclosure is buttoned up. In that case, it's not from the hardtop itself, though, but rather than enclosure panels. If necessary, I can open most of those up during docking if it were to become necessary.... but we haven't had to do that.
Chesapeake Bay, USA