aracheb :
probably ip 51 or 52 i don't think there is much room for an IP 56 or 66 there.
You never know, the Sony Xperia Z is IP57 rated so there's a chance this could be up there too. If it's IP57 or higher then I'm probably going to get it.
Mark Ray :
Nice, but who would spend a fortune for this rugged S4. In my opinion, buying a "Defender" case from Utterbox will make your traditional Galaxy S4 rugged and fully protected and it will only cost you less than $30. http://www.squidoo.com/samsung-galaxy-s4-cases-2
It's probably not going to cost much more than a normal SGS4 and it'll have some degree of waterproofing and dustproofing unlike the case you're boasting about. I definitely believe in the protection of the Otterbox Defender cases since I have one myself on my aging Evo 3D but those are 2 things that they weren't meant to protect against.