The garage was full of it... in a gasser, running without and exhaust will rarely burn a valve (where that old saying came from)... but in a diesel, no problem.
I have ran without a cat for 86k without any issues (other than a heavy right foot to hear it!)... I saw a slight increase in mileage and a slight increase in performance... but I'm not sure if it was the cat, the muffler, or a combination of the two that was the real restriction...
Can't help on the EGTs as I don't have guages.
steved