Not certain what the difference is in the two materials- but 631 is supposed to be the modern 531. Think I would be more inclined to look at the specifications of the components on the two bikes- and there should be a very appreciable Price differential on the two bikes. All I am thinking is that a lot has changed on Components since 2003 and they have improved a bit.

Difference in ride should not be great- if any- between the two materials. So let the wallet and Component quality tell you what to get.

Link to the Supposed difference on the two materials.

http://www.dawescycles.com/c-47-abou...lds-steel.aspx