WOW!....I have a 1.4TC MKIII....for my 70-200mm f/2.8L IS II...Answers:For somebody who uses 16mm as often as you do get the 17TS-E. If you want a bit more flexibility with minimal loss in IQ then get a 1.4TC MkIII.
You can use the 1.4TC MKIII on the 17mm TS-E?
What is the IQ like?
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!