Feeder Wire Ampacity
Here is the code references per 2014 NEC: 110.14.C- Conductors with temperature ratings higher than specified terminations shall be permitted to be used for ampacity adjustments corrections or both. 
215.15.A-  where a feeder supplies a combination of continuous loads or any combination of continuous and non continuous loads the minimum feeder size shall have an ampacity not less than the non continuous loads plus 125% of the continuous loads.
Table 310.15.B.3.A- adjustment factors for more than 3 current carrying conductors.
4-6= 80%
original comment:
I don't have my code book handy so I will post this as a comment. You can use the ampacity of the wire at 90 for derating but you can not exceede the 75 deg table for a final value. Also if your planned loads are continuous (+3 hour loads) that portion of the load needs to be at 125%. Unless I am setting up a sub for a dedicated non continuous load I use 125% of the feeder breaker size. But using the specs for 90 deg and derating is legal.