I agree Reno, and as for which column you go to the code reference associated with the tables is 310.15(B)(2) for starters. If you have a THW conductor go to the 75° to start with and derate as needed. If the wire is XHHW start with the 90° column and derate as needed. There are a number of rules pertaining to derating found in 310.15(B)(1) through (6). The NM Article 334 is no exception.
