SA-105 vs. SA-266 Cl. 2 1

In my opinion, SA-266 Cl. 2 is not allowed by Section VIII Div. 1, see Section II. B16.5 does not allow this material for flanges.

Of course SA-266 Cl.2 is allowed under Section VIII Div.1.
The two materials are quite equivalent in my opinion: only minor differences in the specification (heat treatment policy for instance).
I think the choice is a matter of taste, or, better said, of continuity at client's organisation.
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The ASTM A266 class 2, is not allowed by ASME VIII div.1, infact if you look ASME IID, this material is underlined NP (not permitt.) under VIII div.1.

The 2001 Edition of ASME Section II, Part D was revised such that SA-266-2 is permitted to a maximum temperature of 1000 deg F for Section VIII-1 construction.

I remember these two grades as generally used for flanges and other applications like tube sheet etc., On the former, there is a max limit in weight of 10000 lbs (this is old, rusty recollection of mine, I am not sure what the current code says...) Sorry if I have mislead anyone with this...