Irrelivant. It's all about sound signature. HE-500 from everything I can tell is leaning toward neutral and natural sound while the 400 is more musical and fun. Frankly for the price difference I don't see the point in HE-500, but that's me.
E17 is fine, but you will need to upgrade eventually if you actually want to hear what the HE series can do, if it's just for portable use, it's fine.