Awwwww yea! Just got myself an Asus RT-AC86U with Asuswrt-Merlin and the OpenVPN client configured in there gets me a hair line below 30/10 now. Thank you for that suggestion!
I'm like to think that considering its hardware the RT-N56U should be able to handle such a speed using OpenVPN. However, its hardware doesn't differ that much compared to the RT-N16 and that didn't perform quite remarkably.