Would you be interested in a governor with a performance guarantee?
If so you should check out the MicroMiser beta available here:
It is much more sophisticated than the simple threshold based solutions.
If you wanted your VM to have an IP and appear as if it is a real machine on the network many people used to have to follow the 100 odd lines of documentation here: https://help.ubuntu.com/community/VirtualBox#Networking
Now they can just start it and it works out of the box.
It was pity stayed his hand. "Pity I don't have any more bullets," thought Frito. -- _Bored_of_the_Rings_, a Harvard Lampoon parody of Tolkein