Serious reds under screwcap?

The other night I undertook a small experiment. New Zealand wine producers Vidal, part of the Villa Maria group, had sent me out of the blue a few years ago 12 bottles of Vidal Estate Reserve Cabernet Sauvignon 2000 Hawke's Bay, one of the impressive Bordeaux reds made on the so-called Gimblett Gravels (see Gimblett Gravels v Bordeaux, a blind tasting comparison of them with their peers), half of the wine having been stoppered by natural cork and the other half by screwcap. They said they wanted me to experiment with the effects of the two different closures...