In this case it is Taiwan because that's where the frames will be made, and I don't know if it's seamless. It's not that he refused to tell, but that nobody seems to have asked him. As far as the conventional wall thickness criteria, I tend to agree with you, but this is what he said he's doing. Just based on price, it's not Kaisei. I'm well aware of the conventions set by 531, but the convention set by Columbus SL is for 9/6/9 in all three tubes. And some makers, notably Trek, deviated from the 531 standard. DT was 10/7/10 rather than 9/6/9 at least in the 1981 through 1984 531C and 531CS, if one may believe their brochures on Vintage-Trek, and I see no reason not to.

And (I think I said) I've ridden bikes with both the Trek 531 (my 1984 610 with original fork and a special Dediaccaia high-rake 60+ mm fork), and my former Woodrup with (as marked) standard 531 tubing and the early fork blades (Imperial?). The 610, even with the high-rake fork, is still stiffer than the Woodrup, in terms of bump tracking. So I'd say your keel design info is accurate, but for this bike I'm looking for more flex. See the posting above by Six Jours, who's built a few LD bikes, regarding flex v. noodling.

But really my original point in starting this discussion was to gain input on whether the chosen wall thicknesses should be implemented in a heat-treated steel or a standard 4130. My question was not based on ride quality, since flex properties are not affected by heat-treating and should not be expected to change. What may be expected to change are durability and crash survivability of the frame.

That's actually not a question anymore, since the builder has announced in his blog that he's changing the design spec to a heat-treated steel.

If you'd like to dialog with the frame company about their design, pm me and I'll give you their info. No need to drag them through anything here - my question is more about appropriate frame engineering than anything else.