As someone who builds steel gravel bike frames as a hobby, I can tell you that anything shorter than 425mm is very difficult to achieve and still have clearance for wide tires and a road crankset. At less than 425mm, there is also the possibility of the tire contacting the seat tube with a 73 degree seat tube angle and a large tire like a 700x47. A curved seat tube can solve the seat tube contact issue, but the further forward you push the tire, the less room there is between the tire and the chainrings. Titanium adds to the problem by requiring larger diameter chainstays that don't dimple easily for tire clearance..
I normally do 425mm on my frames. I go to 430mm for a larger rider that requires a slacker seat tube angle. On 650b frames I usually do 420mm stays.