Notes:

I have a suspension seatpost. Thudbuster LT hooked up to a B68 saddle. However, my feet and hands are not supported by this platform.

My 700x38 Schwalbe Marathon GG measures 39.5 mm on my 700c Velocity Chukker rim, and is about the same height.

I have room for up to 700c x 42mm tires. I've seen other Vaya users run 650b x 56 mm tires with room to spare. The overall wheel diameter is only 8mm different with 650b being smaller, the BB drop should be fine.

I am commuting in a city with notoriously bad public transportation. It would be slower to take the bus, quite literally.

The Salsa Dos Niner posted below is the kind of bike I'm considering. I have read that this bike will eventually crack somewhere in the frame due to the suspension design. If there is another soft-tail like it production that is not a $4k Moots YBB please let me know.

I am anticipating 9000 miles of commuting this year. I need DURABILITY. I'm leaning more towards a new bike very much like the Salsa Dos Niner than kludging my Salsa Vaya.

The Salsa Vaya is a sweet bike. I am very happy with it and I've ridden it about 10,000 miles. It's just not the right bike for the job in this instance.

Question:

How low of a PSI could I roughly reach with 700x42, considering i'm 225-230lbs, and my bike is balanced 40/60?