If price is of no concern, I'd go with the 3v and have Bos heat treat it. If price is a problem, 5160, L-6, or 1075/80. If it was a knife I was forging for myself, I'd just use one of the old leaf springs or a piece of one of the old saw blades I've got laying around. If it was for a paying customer, I'd use new steel. I'd also go with a little thicker spine, unless it's mainly going to be used on softer stuff.
Todd