Actually with steel it's fatigue is forever, provided you stay within it's limits. Titanium has a propensity to develop cracks from scratches. Carbon fibre is great, provided you have an excellent frame builder and don't damage the laminate by scratching it.

As for 953, it sounds great, huge UTS, good elongation( at least 10%) etc. But then you read about how the previous wonder metal, another maraged steel from the same manufacturers - Carpenter, had severe problems when cutting and mitring the tubes, the tubing was so thin (953 weighs the same as cr-mo, you just use less of it) the tubes tended to crush, and they're claiming it has good dent resistance?!
Maybe they have solved the problems, but I'm remaining sceptical for now.