By far the biggest impact on tunneling over DNS is whether or not you can make direct DNS queries to the server running iodine. I did some tests a while and fo

By far the biggest impact on tunneling over DNS is whether or not you can make direct DNS queries to the server running iodine. I did some tests a while and found that iodine was ~98% of non-tunneled speed when I could access the server directly, since then the traffic is wrapped over huge big TXT queries and it's really efficient. But the common case for using it is that you can only lookup through a local DNS server, and then it's usually ~0.5% or so of the usual speed. I.e. 1-2KB/s at best.