The installation process on your link was very similar to the one on the Ubuntu site. I recommend the MultiRom approach so that you can continue using the device as an Android in addition to testing Ubuntu.
As far as speed is concerned, the first thing you need to do is get away from the Unity desktop which is slow. Install the LXDE desktop and the system is pretty fast. Running Ignition as a client under LXDE is good and data entry went fine. I expect that it would be even faster if it was running Oracle Java but I am stuck on that one for now.
I initially tried to use OpenJDK 1.7, it worked but it wouldn’t allow me to hide the windows menu bar when running the client. I noticed the same problem on 1.7 on the x86 platform so I rolled back to 1.6 and voila it works just fine.
To keep you from losing your mind typing on a touchpad keyboard on the Nexus, set up remote desktop connection using vino and then do all your testing/programming on the remote connection