The thing that surprised me the most is that the 645/35mmSchneider combo doesn't outperform the 35mm/24mmCanon lens one, in terms of distortion.
If anything the walls look more bowed in the former.
I'm very close to spending an awful lot of money on a Silvestri/Rodenstock/phase set up in an effort to make interiors look more natural.
I'm having second thoughts.
The 35XL has less distortion than 24mm Canon (the Canon is not too bad though). I'd guess that the 35XL shot is done without distortion correction, and the 24mm Canon is done with. From measurements/data sheets: the 35XL has about 0.5% barrel distortion in its 90mm image circle (I'd say only 75mm of it is high quality though in terms of sharpness), and the TS-E24 has about 0.9% (which is not bad, not sure if it's entirely comparable though as the TS-E24 number is only for the 44mm image, I'd guess the true number is more like 1.5%). Due to the simple symmetric design of the 35XL it's not surprising that it's lower than for the heavily retrofocus TS-E24. In fact I would guess that the 35XL is the lens currently on the market with the least distortion of comparable focal length and image circle.
If you're worried about distortion note that the retrofocus Rodenstock lenses can have some, take a look at the data sheets to get an idea, the 23mm reaches 2%. Retrofocus design has many advantages but one of the disadvantages is that it introduces distortion.
(I own both the 35XL and the TS-E 24 lenses so I could make a test for you if you want to, I'd suspect that the TS-E24 distortion would detoriate more in shifted positions than the 35XL. I'm very pleased by the low of distortion in my 35XL, but I generally shoot landscapes so I'm not looking at straight lines as often as an interior photographer... attached a few examples of the 35XL with straight lines I happened to find in a quick browse, some with substantial shift, none of them is distortion corrected. The bridge might look a bit distorted anyway, because the bridge itself is distorted