And the string on the OPV IS a little small for cold water/dry gloves, but it is doable. Another option is the Agir wings. They seem just as nice as the Halcyon stuff but they are a little bit more cold-water ready.
I have the Agir Niord 20kg (44lb) wing, and while it's extremely durable and well-constructed, I've found that the OPV is positioned in such a way that it can be more difficult than an Evolve or DSS Torus to dump gas from it while in trim - it requires a slightly more exaggerated butt-lift-tilt motion in order to vent.