The only difference is the fan. Not sure how big of a difference would make.
I've read up to 3 degrees. Worth returning for that difference? I'd probably end up receiving it on Monday.
I would definitely return it, it's just that I just received my FX 8320 and I'm eager to set it all up. If there's no real difference I'll probably just keep it. I'm not in the least surprised that amazon fucked up though. lol.
It seems that the PLUS has higher CFM, although since the EVO performs better I'm sure it would just be louder. Honestly, I think I'll stick the stock cooler on for this weekend and return the item, see if I can get the new one by tomorrow or Monday. :s