It sounds like D2 is exactly the right choice for your stamping die. It’s a high-chromium tool steel, so well-suited to being used with stainless. Also, since your process will be at room temperature, just use the “right” (cold-work) tool steel for that temperature. Regarding your concerns about wear over 500k cycles, there are some generalized performance results out of Germany that suggest the die may see wear rounding at about half that production run (250k cycles). However, I don’t think you’re going to get a better performing alloy; D2 is perfectly suited to this. I think you’re trying to get too fancy (to your own detriment) if you want to try to use a hot-work steel for this stamping.