I think of it more in terms of twist instead of camber control. With the mainsail cleated forward, you are pulling more aft on the foot (flattening the foot, like Matt said) but also, the leach can twist off. Cleated aft and the leach is firm. I pretty much always had it aft with two sailing (400 pounds of people) and used the traveler to depower (up to about 25 kts windspeed). Single handed I was more cautious and would only use the aft hole when winds were light. I suspect there were times when boatspeed suffered because of hole selection, but it is something you can't easily change while sailing in big wind.
I don't think the clew holes did that much with camber in the main...that was more a function of mainsheet tension and mast bend...when I looked up to check the sail it was pretty much always massively powerful whichever hole I used. I did like the sail shape on the Getaway.