Definitely leave the bailer open on a downwind run!
I tend to close the bailer on flat water and only open it when needed - but in waves I always leave it open.
I suspect that the difference in drag is so marginal that it's more a mental drawback than anything real - unless you're an elite paddler!
Rob
Currently Epic V10 Elite, Epic V10 Double.
Previously: Swordfish S, Evo II, Carbonology Zest, Fenn Swordfish, Epic V10, Fenn Elite, Red7 Surf70 Pro, Epic V10 Sport, Genius Blu, Kayak Centre Zeplin, Fenn Mako6, Custom Kayaks ICON, Brian's Kayaks Molokai, Brian's Kayaks Wedge and several others...