I've tested them side by side many times and love both, I do however only own Odeur 53. I'm planning on getting a bottle of 71 as well, but for some reason other fragrances has come before that one. It has been about a year since I last smelled 71 though so this won't be a much detailed impression. Hopefully I'll be able to argue a bit about my view further down the line
Odeur 53 is clearly the most versatile of the two, being almost obnoxiously clean. Well not really, but it is a very clean scent, still with a few interesting twists.
What Odeur 71 shares with 53 is the ozonic metallic ringing mostly, and well, it also feels quite clean (like a fabric softener). It is however deeply floral instead of only being clean. I have no idea if 71 has hedione in abundance (http://boisdejasmin.typepad.com/_/20...nce_ingre.html) as 53, the jasmin like chemical also used extensively in Eau Sauvage.
I really NEED a bottle of Odeur 71 to freshen up my impressions, but it really is a lovely fragrance.
Edit: Oh and I don't put much into those words CdG has used to describe the fragrances... They put them forward as notes, but I see them more as guidelines for the us to use when associating around what the fragrance could be. Odeur 53 sounds so WACKY when reading the notes and I remember Chandler Burr name it has completely unwearable, but to me it is one of my most used fragrances and also the one I consider most appropriate for most occasions.