I'll give you 1 to 4°.

My books say 10° WITH VACUUM DISCONNECTED. When you disconnect and plug
the vacuum the idle drops so low the engine won't run reliably.
Interestingly enough the vacuum advance counts for ~5° at the distributor or
~10° at the crank. So rather than adjust the idle up because of disconnecting
the vacuum, and then having to adjust it back down when the vac is reconnected,
I set it at 20° or a bit more with the vacuum connected, which complies with
the intent, if not the letter of the book.
Total advance runs to about 35 to 37° depending on the advance curve and
(more importantly) the condition of the elderly distributor advance mechanism.

I agree that 0.002" is not much of a change in valve lash, however it does
amount to about 0.003" on the other side of the rocker arm, and if for some
reason the valve stem expansion and other factors eat some of the lash up to
the point where the valve seat pressure is reduced it does have a major effect
on the conduction of heat from the valve to the seat. I have always used stock
valves, which I assume are not stellite-faced, and under similar driving with
0.020" valve lash, have not experienced the burning and cracking that I did
experience with 0.018" valve lash. This was on exhaust valves only and was
not accompanied by seat recession.
--
George Downs Bartlesville, Heart of the USA!