I spent a lot of time last week on a bareboat in BVI trying to find the best downwind combo with just a main and Genoa. The swell made it look as if we were particularly susceptible to gybing if I didn't rig a preventer to go wing and wing and going deep into the wind the main blanketed the genny and it was impossible to keep full.
In the end if I was in a hurry (ok, I never really got in a hurry) or the wind was pretty light I'd rig a preventer and go wing and wing. I did spend a couple of hours rigged that way othwise I'd just drop the main and run on the genny. Just remember to to move the fairleads around to keep the top of the sail from luffing.