The pricing doesn't tell us much. Why do you believe that 400i uses the same driver as 400, only tweaked? It could be, but some proof would be nice (though I'm not sure how it affects the discussion either way). The rest just sounds like an argument from authority. No one here gives a shit about that.

I thought the tweaked drivers was a well-known fact and was acknowledged by HFM.  I could be mistaken and don't really care to go dig it up.  As you said, I don't think it really has any bearing on the discussion.

marhol, technical abilities be damned.  Listen to them and make your choice.  Great technicalities are pretty meaningless if the headphone doesn't allow you to connect with the music.

In case you want more input...

I chose the HE-500 (with jergpads):

1)  Yes, the 400i has tighter/clearer bass.  The difference wasn't so vast to me as to make it a deal breaker.
2)  I prefer the 500 mids without question.  Smoother and more natural. 
3)  Vocals.  Again the 500.  The 400i pushed vocals out front and made them sound a bit unnatural.  When I first heard the 400is, I thought the vocals were a little hot.  After I got used to them, I decided I was mistaken.  Then, after comparing  directly to the 500, I realized that my initial gut instinct was correct...the 500s have the vocals a bit further back, but they sound more appropriate to the music. 
4)  The 500s are smoother and more mellow across the range, which I ended up preferring.  Despite the smoothness, they still tend to do a credible job with fast, energetic rock.  Not as lively as the 400is, but certainly good enough.
5) Voodoo magic? The 500s have this way of making live music sound like you're actually there.  I don't know what to call this...all I can say is that for artists whose live shows I've attended, the 500s do a better job of recreating that experience.

Someone over at the other site compared the 400is to a good craft better and the 500s to a smooth bourbon.  Silly analogy, maybe, but it works for me.