Could you feel a difference between a 531 frame and a gaspipe one, all else being equal? Almost certainly, yes.

First, the various iterations of Reynolds, Columbus, Tange, Ishiwata, Vitus, True Temper (have I left any out?) steel alloy tubes will give superior rides because (1) they are stronger than garden-variety steel alloys which means that (2) frames can be built lighter while retaining the same - or greater - strength, which also means that (3) you can get that great, lively "steel is real" feel that folks (me included) rave about but have a hard time describing in any objective, measurable way.

I am convinced, however, that once you get into the good steels, how much you like the ride is going to be more a matter of the skill and artistry of the framebuilder and designer than of the type of steel. Yes, the type of steel can make a difference, but how it is drawn (thickness, length of the butts or tapers, shape or shapes of the cross-sections, etc.) is likely to be more of a determining factor than the composition of the particular alloy. Of course, I have never built a frame (putting a lit torch in my hand is a really, really bad idea), so I may be completely wrong about this.