FWIW, I have been told by multiple builders that stainless is very hard (physically) and does not have the same feel as high-end non-stainless steel from Dedacciai, Reynolds, or Columbus. If you're worried about rust, buy a can of T9.
A modern steel bike with T9 will outlive you.
Before going stainless, talk to the builder about what you want and why. Mine talked me out of it, and I don't regret it.