WOW!....I have a 1.4TC MKIII....for my 70-200mm f/2.8L IS II...
I say WOW because...I have been saving for the new Zeiss 15mm f/2.8 ZE...and then..I got to thinking I could buy a Canon 17mm TSE, save $700-$800, have the tilt and shift, comparable image quality (right?) and the 1.4x set up would just be a bonus. (I never thought a 'tele' converter would work well on a SWlens.
hmmmmm....I will have to think about this more....DAMN!!!! LOL!
I have never used the Zeiss 15mm, but I regularly print 3 foot panoramas from a single shot from the 17mm TS-E and the IQ is as good as your technique. Of course the Canon lens does offer vastly more functionality than the Zeiss, not least of which is the shift stitching option which ends up giving you an 11mm lens fov on a 50mm x 24mm sensor, or the ability to use your 5D MkIII as a medium format equaling 44MP 36mm x 48mm sensor.
Yes...I am aware of that...when I started to compare the Zeiss to the 17mm I came across the 11mm "bonus".
How well does that crazy front element hold up???