Nowadays, i think supplier is very important,
loads of steel out there, not all equal by some stretch,
Krupp 55 was used for years by a well known Italian sword maker, now i think they use 6150 or 50crv4, would have to double check,
as do a few of the premier English makers,
any sword steel will make a good spring, not the same for knife steel though, a good many yes, but not all,
5160 EN45 -47, etc etc, a lot of the spring steels are interchangeable within both industry's,
heat treat is hugely important,
majority of spring company's really know their stuff, sometimes underthinking it, and letting the company do the spek work is the better option,
or if local, dip the scrap bin and have a play,
if you want super special, there are some impressive smith-metallurgist's out there,
interesting thread,
boing,