Touring - 631 for touring frame

Now that the classic 531st is unavailable, ive been told that as a frame material, 631 is the best alternative to make a frame for touring in, does anybody have any comments on this from personal experience or tech know how.
Im planning to use it in a pan am. trip if that helps, it would be built as a sloping top tube, 26 in wheel tourer, in case it helps with advising.
Cheers take care all

I notice that some builders are still advertising 531 frames, some have switched to 631 and some to 525 or a custom selection. Some of the builders may have quite a stock of the 531ST pipes if that is your preferred choice. You might like to contact your favourite companies and ask them. Traditional touring experts, like Jacksons, Mercian, Steels etc., might be a starting point.

[Thanks, ive ordered a bob jackson tourer. It is 631 main tubes with a 525 rear triangle which they say is a less tempramental steel to be welded anywhere , he said that sometimes 531 was a bit dodgy.
Well im well chuffed with the service they have given in there. Im happy as toast

I used to live in Leeds, equidiatant between Woodrup's and Bob Jackson's........ talk about spoilt for choice! What with the proximity of Pennine in Bradford and Ellis-Briggs in Shipley, the place was a veritable nirvana for custom frame afficianados........

I can imagine how you must be feeling, as you await delivery of your frame! And the anticipation is tempered by the knowledge that those guys really have the expertise you are looking for.........