I've bought OEM and pattern wings off eBay recently.
Both pairs are brand new. The difference in construction quality is clear, although whether this means difference in fitting quality I don't yet know. I won the OEM wings at about half retail price; the pattern wings I won at a discount of about 90% off their manufacturer's price.
The pattern wings are Hadrian; I have a suspicion that Hadrian and Beevers are part of the same organization, as I think I saw the former featuring as part of the latter somewhere on the Web. I've seen favourable and unfavourable comments on pattern parts, many saying that they are fine, perhaps with a bit of fettling, and others keeping the OEM faith (which I am normally inclined to do).
I'll weigh both pairs and will let you know whether there is any difference.
I've also bought several used OEM wings, all corroded around the fixing holes to remediable degrees. When the time is right, I'm going to offer them all to the bodyshop to see which they prefer. The surplus ones I will then sell on, and will post them here and in the MB Club before going to eBay.