[supersleuth]

OK, got my $99 HF5 from Amazon and am now listening to a very familiar Mahler recording. I agree with those who say the HF5 is a pretty significant step up in sound from the MC5. Not only does the greater treble extension of the HF5 make its sound noticeably more open and transparent (which I expected), but to my surprise, it also has more bass impact. All in all there's considerably more of the "you are there" feeling that I love from my Grados (SR80 with bowls). Also, the thinner body makes it significantly easier to get a good deep insertion.When you can get it (as I did) for $40 more than the street price of the MC5 it's a no-brainer. I'd still be willing to recommend the MC5 as very solid for its price to those on a very tight budget, or who are getting their first IEM (as I was when I bought it) or first deep-insertion IEM and want to start out with a minimal financial commitment. But mine will now live in a drawer as an emergency backup. The only negative I see with the HF5 is that the cord is considerably more microphonic- I need to not only use the shirt clip (which I always have) but also cinch the cord up closer to my ears than I did with the MC5 to keep it from rubbing against my collar. Then it's not an issue.