Not to be pedantic, but I am not sure what relevance if any your quesiton has. All the Reynolds steels are similar...the higher number offerings simply have higher yield strength and therefore can run thinner wall to achieve the same section modulus. The most common way to achieve more strength with steel is alloying, more carbon and/or heat treating. Reynolds is very protective of their steel composition...it is proprietary for obvious reasons. All said, you will be hard pressed to tell the difference between riding two similar bikes with frames from either...one with Reynolds 631 and the other with 853. 853 is great stuff but you would likely not feel any difference other then a few grams of weight.
George