Hi AirVpn does work at almost full speed for a VM 120 connection http://www.speedtest.net/my-result/2952551578.
There are however a few caveats my speed does vary sometimes It goes as low as 12 Mb/s. In peak times it is common to see it at about 50Mb/s. I suspect this is part due to virgin and in part due to air.
It is worth noting that virgin tends to handle congestion on a per thread/connection basis. So at a congested time you may only get 60Mb/s on a single connection/thread but if you have two you will still be able to get 120Mb/s. It is my assumption that the AirVPN VPN tunnel is effectively a single connection in the VM world so even if we run two threads over the VPN tunnel it is slowed as if it were a single VM connection. In the past (years ago when I last looked) Speedtest used two connections to test speed, so I would not be surprised to see airvpn running at half VM speed at a peak VM time. Congestion on VM can of course vary massively minute to minute. It is also worth noting this slow down will effect bittorent with its multitude of threads even more significantly.
Secondly OpenVPN is cpu intensive. On my tomato router (asus rt-N16) it was limited to about 8Mb/s, I doubt the asus rt-N66U or 56 would be much faster. Even an intel i860 caps at about 90Mb/s. My SandyBridge 2500K can handle full speed 120, either using the airclient or a virtual pfSense router.
I would also expect any cheap all you can eat VPN to be limited at peak times, or become so as people discovered it.
Please take my comments with a pinch of salt I'm not a network expert, nor have I had my views confirmed. They are just the way I figure things to be, any reasoned corrections would be welcome.