True that 135 and 33x44 format systems are giving excellent results suitable for most professional work even these days.
However, being Dante's Inferno here, I would suggest a tech cam set such as the ALPA 12 Max (simultaneous vertical and horizontal movements) with the Rodenstock 32mm lens which closely matches your required field of view on a digital back with a crop sensor such as the P45+.
The P45+ represents excellent value these days and hence the digital back I'm recommending you to start with. It takes long exposures like a champ as long as you keep things reasonable (i.e. within 10min), otherwise battery life will be of concern and this is speaking from experience.
The way I look at it is that the tech cam and Rodenstock gear gives you the absolute best image quality possible (and believe me, you will be able to tall a difference, especially when printed) and being non-digital products, they're less prone to drop in value which means that after some use, you'll be able to shift them with minimal losses. Whereas with digital camera's such as the X1D or the GFX, the resale value, once a succeeding model is launched, is often 50% or more less than the initial purchasing price.
I started out with the exact same setup about 3 years ago and haven't regretted it since. The 32mm lens is amazing when it comes to architecture, you can easily shift 15mm up on the P45+ with our vignetting and you can even get away with not shooting the LCC most of the time. If you want to check out some samples, you can always visit my Flickr page, on most images the camera used is right there in the EXIF.
Anyway, just some food for thought....