A Q setting of 0.7 will get you the most output. Sounds to me like you will be happiest with that setting. Also, using the sub with both ports open and the EQ switch set to 'EQ2' will get you the most headroom. If you are really pushing it hard, use it with both ports open and 'EQ2'. It should be hitting pretty hard in an 11'x11' room. Hell, you could always run it hotter than 3dB, if that is your tastes. I know that sometimes I will run the subs pretty hot.
You could always add another or upgrade to a more powerful sub as well, but the thing is, the VTF-2 mk5 should be able to keep up with the system gain level in a 11'x11' room pretty easily. You would have to be listening at very loud volumes in order to run up against the VTF-2 mk5's limits. I'm not saying its impossible though.