My EGT begins to climb when I go above the 12.4 AFR mark too but unless I have timing way low or am running too lean AND high load, they don't get crazy high. I'm measuring pre-turbo so I guess there is maybe +150-200F difference? What kind of peaks do you see?
Your car is so amazing! I love "tuning in" to your threads to see what you are working on...Those new headers are sweet looking, I hope they net you something substantial beyond the obvious cool factor.