BSA built the Ti framed Moto-X bike after Jeff Smith won two World Champs in the mid 60s. It was a bit lighter, and a lot more flexible, and the constant cracking induced by the extra flexing, required welding in a special inert atmosphere, thus requiring a special portable chamber were two of the features which made it an expensive and very dead end.
I'm pretty sure that I read an article either by Ken Sprayson, or an interview with him where he stated that there wasn't much difference between Reynolds 531 tubing, and T45, apart from sometimes varying availability and minor differences in cost. In the same article he said that "ordinary" cold drawn (i.e. high quality) carbon steel and 531/T45 tubing differed in that the 531/T45 tubing lost less of its properties after welding, all materials loose some of their properties, but some loose more than others. This was in the days when frames were gas bronze welded. 531 tubing has a yield stress of about 550 MPa, T45 has a yield of about 480 MPa, cold drawn 1018 steel tube has a yield of about 310 MPa. If you take the yield stress as a determining feature, then if 531 is 100%, T45 approx 87%, 1018 approx 56%. Reynolds 531 has been pretty much unavailable for several decades, except to "special order" and we all know what that means $$$$$$$$$$! Apparently, these days AISI 4130 is considered to be comparable to R531. This goes some way to explain why Manx featherbeds are lighter than road going featherbeds, the Manx frame is thin wall 531, the roadgoing frame is thicker walled cold drawn steel tube
Springback, all materials suffer in some degree to "springback" when bent. It's how that springback is catered for by the person doing the bending that makes the difference. Its one of the reasons that some frames are constructed from straight or largely straight tubes. Bending a tube accurately in one plane is pretty specialised, bending the same tube accurately in 3 planes is close to artistry.