hmmm im not too sure about that all. we race here and the engines seem to last 1-2 seasons on a refresh, about 3-4 seasons for a full rebuild. and yes they are running over 10k rpm lol. but yes after time high rpms will do their damage. its just like running at lower rpms for a longer time really, you just notice the loss more when it happens faster(at high rpms). our engines usually stay competative in in the novice and expert level for at least 2 seasons.
back on topic.... when you got the PCIII tuned how did they adjust for air/fuel ratio?? did they use EGTs or a wideband system? if they used a wideband system then did you drill another spot for the sensor up stream of the catalytic converter?
if they just put the sniffer on the back then its reading a false signal. the cat will be burning up all the hydrocarbons which causes the air/fuel ratio to go lean. the tuner sees this lean signal(unknown to him its wrong), then compensates by adding more fuel until he gets his ideal afr.
whats this mean? your engine is running rich as hell, and is incorrectly tuned. you will not see black soot on your tail pipe because all the hydrocarbons are being burned in the catalytic converter.
now this is all irrelivant if the engine was tuned correctly or if you removed the cat before tuning.