Only thing I can offer for your question barry is support that I also have very high EGT's in the upper RPM ranges
I can crest around 975C by redline (8000rpm on my FC block) at 20psi (T04-R, 67mm compressor.....1.00a/r divided rear)
I've also tried a number of different things to reduce the temps, but I'm starting to think that perhaps back pressure is the real culprit for the high temps...unfortunately I do not yet have this parameter monitored in my car
The largest difference between my car, yours, and howards, is the fact that he has nearly DOUBLE the turbine area, and exhaust area and volume we do. And his EGT's are reportedly solid and *much* lower then what you and I have found.