Anyway, where did you get this info on the E-M5? BTW, what is the E3 and E5 IP rating? In any case, I have taken a tumble into surf at the beach while holding my E3. The E3 was completely underwater momentarily and when I recovered, it was all wet, as well as I was, with sand all over the camera.
I just continued shooting and when I went back to the hotel a few hours later, just washed it off with tap water (to remove salt and sand residues) and then let it all sit dry. The E3 din even miss a heart beat throughout this thing. Continued to work as if nothing happened. That must give it an IP rating of at least 4, plus its salt water...although the duration of exposure was not 5 minutes.
But I would say that the rating is probably a little conservative. For sure, I have used the E3 in torrential downpours with the camera helds lens down. That should be a good IP rating of 3.
You can find it in the user manual, in the specifications section near the end. Strangely, the E-3 and E-5 manuals do not mention weather-proofing in the specifications.
Then again, I think the IEC IP rating is not that important in actual use. I have shot with my non-sealed EOS 60D and 15-85mm lens in the rain and in front of waterfalls. No hiccup at all. Most enthusiast to semi-pro DSLRs are at least drizzle-proof. They are certainly not "made of tofu".

Quoting Olympus: "Thanks to extensive use of ring-shaped seals throughout the body, the OM-D offers the same dust & splash proof durability as the E-5 within a compact and light-weight body. From normal shooting in the rain to more extreme environments, the OM-D lets you focus on shooting by protecting the camera against sand, dust, rain and splashes." This should be enough reassurance.