The only thing that I can add to the consideration is the difference in format dimensions between the 6x9 and the 4x5. I always thought the 4x5 blocky at 1:1.25. Landscapes, to me at least, just look better when wider, where I look at the 4x5 frame as a nice portrait dimension. Now this does not mean that there aren't a ton of great 4x5 and 8x10 landscape pictures, cause even a 1:1 format can look great if composed properly.
If you find yourself use to the longer frame which incorporates more, you may just find yourself starting to shoot wider lenses on the 4x5 as I did, and of course that pushes the subject matter back and widens the near far perspective. So all in all, it's not just that the working characteristics of the 4x5 may be slower for most, it's adopting a different perspective in your photography. I'm personally returning to the 6x9 format in the baby Graphics; I like the smaller body sizes and the compression I get in using a normal to wide 4x5 lens in the smaller format especially when out in the American west. It's just something to think about and of course it can be overcome by cropping. BTW, the sheet film camera really lens itself to self developing with the cost of sending off to a lab much higher nowadays, and of course the restricted selection of good color films at decent prices.