While I don't have anywhere near the experience that a guy like Kirk has, I have done a fair amount of architectural work for ads and brochures. I don't like working for most architects though, which is another topic. By art directing the shoots myself, I avoid getting pushed by an inexperienced client to "get it all in one shot" and can avoid using the goofy superwide angles that most mid-level commercial architectural shooters have to use to satisfy the client requests. Note that the esteemed ESTO - HB shooters hardly ever use the superwides, at least for their portfolio shots.

That said, just get a late model Rodenstock Grandagon 90/4.5 and use the heck out of it -- along with that nice 150 Sironar you already have. Keep it simple and save your money until you need some other lens (or a Noblex or DLSR or some other item).

The faster, more expensive lens is easier to focus, has more coverage, and is more even without a center filter. It is large, but so is everything else...

As for using roll film, if you are not shooting at Kirk's quantity and it ends up forcing you to buy a couple of $1000 lenses, then is it really a savings afterall? Readyloads are expensive per unit substitute for a roll back, but you can buy a lot of them for the cost of a $500 6x12 back and a couple of extra superwide XLs or Grandagons.