I've found from my own use of the Canon TC's that the 1.4 is a much better item than the 2x. however you have shown here that its quite capable of brilliant results...
This thread should serve as a lesson to others, Upsampling by 2x is a no go... When in doubt, spend more money!!
More seriously, it does show very well the degridation to data after being stretched after the fact as opposed to using either a TC for photography or a barlow/powermate for webcam imaging.