One thing to note, I am running two USB NICs on my box with UTM 9 in a HyperV instance and I am able to max out my FTTH connection (84/85). I have a Mac Mini with two j5 Create JUE130 USB NICs (http://www.j5create.com/our-products/ethernet-adapters/jue130.html) and the built-in NIC.
I installed this Trendnet TU2-ET100 USB NIC as a second adapter in my atom pc (AspireRevo R1600) and it works great as the WAN adapter. My WAN speed is 30/30 and my cpu usage stays low with lots of streaming/multiple users. It cost me about $13 on Amazon.
Hi! I tried to use the Trendnet TU2-ET100 Adpater with the recent v9, but while install this USB nic will not be recognized (as second network device on Acer Revo R3600).
Ubuntu 14.10 will recognize this adapter as ASIX Elect. Corp. AX88772.