One thing I know is that I'm your man. I just happen to have some 2x3 Centuries that I'm using for some projects and hence have left over standard lenses that came with them (Graftar 103/4.5); I have several 4x5 Crown Graphics with either Graphic or Graflok backs and either side mounted Kalart or top mounted range fingers, with their original lenses (yes, 135mm-ish Optars), AND I have a 6x9 roll film back for the 4x5 backs.
If you're interested in all of this, PM me, we can discuss a deal.
I love my 105/2.4 on my Pentax 67II, so 135mm on 6x9 isn't too long.
In terms of size, you will definitely save by going 2x3, it's like half-size.
Another thing you should remember about the 2x3, though, is that there is no simple way to shoot instant film, as there never was a Polaroid back for the 2x3. For 4x5, there's both 3x4 pack film adapter (with current film being made by Fuji), 4x5 pack film adapter (unfortunately all discontinued but still available), and the old peel apart 4x5 instand film from Polaroid (expired film available on Ebay).