How to identify engineering sample CPUs

I have read in various threads to watch out for engineering samples of CPUs because they may draw more power, generate more heat, and/or perform less reliably. Can anyone advise as to markings or abbreviations that I should look for on a CPU that would identify it as an engineering sample so that I can avoid them?

To be specific, I am looking at a X5690 or W3690 for a single-processor Mac Pro 5,1.

Also, is there any qualitative difference between the X and the W processor other than support for dual CPU functionality? Nearly everything I have read so far indicates they are equal, but I ran across one benchmark someplace that suggested the W3690 might have been a little faster and that gave me pause.

 

Well OK then - I had no idea that the engineering sample markings were THAT obvious. I guess I don't have much to worry about. Thank you!