Opener records v non-minnow nations
Ryder 36.76 with SR of 100+
McCullum 29.8 with SR of around 90.
Ok, so Ryder's record does come from a small sample of matches (he's only opened on 18 occassions, he's also played another 5 times at number 3 where he's averaged around 50), but that's pretty exceptional. McCullum has a lot more experience down the order, and has performed the role with great success. He's also a bit quicker between the wickets, which counts for a lot in the death overs.
I do concede that with the new fielding rules, Ryder's ability to find the gaps could come in handy in the later overs.