Although it’s impossible for anyone here to really get a feel for your relationship and how she would react to your telling her the truth, remember a couple things when making your decision:
1) People are horrendous at keeping secrets. I would stake very much that if you tell your wife that you PE, her girlfriends will know about it eventually. I’ve learned that even women who don’t seem as though they would, talk about sex a lot more than I find comforting. (This is especially caused by a catalyst woman in the group, i.e., the horny/slutty one. But enough Berkeley psych for now.)
2) This sounds simple and stupid, but you only have to let the “tell her side” get to you once, and you can never untell her. So if you tell her, have it be after you’ve really deliberated and made up your mind—not after you’ve gotten the urge on a whim.
And if after you’ve tried to make it work for a while but it’s not happening, I like sparky’s idea of a half-truth, saying nothing of penis size but giving an ostensible explanation for what you’re doing.
Good luck pal.