I you're on a budget, a frame made of 4130 chrome moly is a nice, sweet riding frame material. Not a lot of difference ride-wise from 531.

A couple years back, I picked up an early 70's Fuji Finest made with their proprietary double butted tubing. That frame, with no exceptions, is the plushest riding bicycle I've ever ridden - and it's pretty sporty and responsive also. They aren't the easiest to find, but they done't break the bank either if you come across one.