Rail meat is among my duties on the boat I've been crewing on. In normal to heavy wind, crew is on the windward rail to help counter act the heeling motion and make it easier on the helmsman. If we're in a drifter, we will sit on the leeward rail to induce some heel, increase lwl and keep the boom from flopping and spilling whatever wind there is.
The point of diminishing returns seems to be around 20 degrees of heel on the mid sized keel boats I've sailed on. If you start heeling more than that, you'd probably be faster if you made whatever adjustment you need to reduce the heeling, even if it means reducing sail. Before reducing sail though you might try adding twist at the top of the main by easing the mainsheet and bringing the traveler above center.
s/v Palmetto Moon
1991 Catalina 36