Redsy,
For the Derating, don't forget the 105ºF attic.
Of course it was not NM cable, but recently seen an installation of 2" RMC on a roof top which had 32 #10 THHN/THWN current carrying conductors on 20A CB's.
The ampacity of the #10 was less than 12 Amperes.
Some loads were greater than 16 amperes and were 24/7/365 loads.
