8% is challenging on 39-25 but eminently doable by most. Just go slower.
I find that even on prolonged climbs, that gearing is sufficient for nearly everything. You do suffer on late-stage crazy steep stuff (Bohlman/On Orbit in Norcal at the end, 21+% in the final stretch!) but it's still doable as long as you keep the cadence real, real slow.