Shawn, I'm sure you are right but I wasn't just thinking engines, more along the lines of TR authority, lively Nr and high pitch angles for hovering OGE.
The rough guide to DA we have always used is DA = PA plus or minus 120T where T is the difference between ISA and the real world temperature in degrees C assuming a lapse rate of 2 deg/1000'. That gives 4560 and 5240 respectively for your examples.
However, the Easyweigh program we use for performance, using your figures, gives DAs of 4243' for 9000' -40 and 5244' for 2000' +40.
What calculation are you using?