senna,
All data I have says that the engines could take far, far more than AH allows us to give them.
Sure, it shortened the time between engine overhauls, but it had no affect in the time frame of one sortie.
A P-38 pilot said that once they were in combat they put the throttle all the way into WEP and left it there for the entire fight, sometimes more than 20 minutes. He said they were told not to, but the reason was not to avoid locking the engine it was to increase engine life spans. Engine life spans are of tertiary importance when you are locked in a life and death struggle 20,000ft over Germany.
A Pratt & Whittney R-2800-59 Double Wasp (P-47D engine) was run at WEP for 90 hours straight without any malfunction. At 90 hours they turned it off, it didn't stop due to malfunction.