If you're trying to run at line rate (or, rather, saturating what it's capable of delivering), you're going to get drops, as each packet is processed by the (relatively weak) CPU. OpenVPN on EdgeRouter-class hardware in general is a value-add-because-we-could sort of thing, good for occasional light use (e.g. remote site maintenance) but certainly not for tunneling web traffic or anything heavier.
Rodney
