In cases such as you describe, I often run several calculations, with and without derates and ATM reductions. I look for a good balance between thrust required, V1, and stop margin.
You appear to be affored a lot more time than most of us. Several calculations?
We use Aerodata; it doesn't take that much time. The default calculations for 2 runways can be done at one time. After that, I can vary the thrust and flap settings to do a "what if". I can do the entries while waiting for the initial results, so there's a "delay" of a minute or less...