Read this whole thread (it might answer some of your questions):
http://www.thehighroad.org/showthread.php?t=225870
I own a SA EMP. Ordered it direct from the Custom Shop since I heard that more than a few persons were having reliability issues with "off the shelf" EMP's. You can read about my experience in the linked thread (page 9 - Post 211). I did a lot of research into the SD ammo. SA told me directly over the phone that they do not recommend +P ammunition, period.
I talked directly to a person that was intimately involved in field testing an EMP (I don't know if it was an independent testing or if it was for SA). However, this person told me that the EMP is quite capable of handling +P ammunition and would (off the record) heartily recommend using it. He went on to say that after his years of experience (he is a LEO as well as a defensive firearms instructor) and research he would only recommend lighter weight bullets in +P for any 9mm application (regardless of gun). He specifically detailed the 115 grain in +P+ or the 124 grain in +P as an ideal load for any quality handgun (except the EMP ... read on). He went on to warn me that any +P+ (or greater pressure) ammunition would "lock up" (whatever that means) the EMP. He specifically said that he would not use 147 grain ammunition because
on average, it is an underperforming round. Yes, he said, there are success and failure stories for almost any bullet type but he was basing it on personal as well as printed research. He also went on to explain the magic 900-1000 fps threshold for bullet expansion and how you lose 75-100 fps for every inch of barrel lost (from the original test barrel length).
To answer your question, he recommended (for performance
and reliability) that I load my EMP with either Speer GDHP (Short Barrel) 124 grain +P or Remington Bonded Golden Saber 124 grain +P. He said that any wear imposed on the pistol from the +P ammunition would be negligible over the life of the pistol with the understanding that you must trade something off (pistol lifespan) for the expected performance of the ammunition.
Finally, I am not an expert by any stretch of the imagination. I'm not a gunsmith and I am not a ballistics expert. If there is anything that I have shared that is wrong or dangerous, please jump in and correct me. I only shared what others have told me or what I have read.