Quick comparison (because I don't have much time tonight) of the SM3 with the FX700...
Used the output from my iPod -> Arrow (which the SM3 now sounds better with since I switched to the Ety tips) and the HUD-MX1.
First, the FX700 has nice bass impact and a nice wide presentation. The mids are filled in compared to the FX500, and the treble has been tamed. But that is a $150 vs. $330 IEM. How about a $330 vs. a $425 IEM?
Both can bring out the bad in bad masters/bitrate songs, but the SM3 is more sensitive to poor recordings.
OK, the FX700, while sounding great, has a leaner sound. Soundstage seems wide, but the SM3 actually exceed the FX700 in width. Then tack on a much better 3D space from the SM3 and it goes from the good presentation of the FX700 to better. For example, Live - Lakini's Juice sounds very different on the two. Presentation of the SM3 is more upfront and around your head while the FX700 is more laid back.
The FX700 has nice detail. Instruments have nice micro-detail, and especially the bass with it's nice natural sounding reverb. It only makes sense though that the SM3 is even more detailed and allows you to easily hear those details since it is more sensitive to poor recordings. I was A/Bing and hearing the clear details of what the FX700 wasn't presenting. The detail is made available IMO due to the better placement within the 3D space, placing everything so well.
To my ears, when going from the SM3 to the FX700, it just doesn't sound 'natural' with acoustic instruments (for example Blues Traveler - Hook). The mids of the SM3 are much fuller and while I don't think the FX700 has recessed mids, when switching to the FX700 they do sound kinda sucked out. And there is a treble emphasis with the FX700 that makes it sound a little off also. The naturalness of the SM3 in comparison with the FX700 is probably due to the FX700 sounding flatter in soundstage depth (and height).
The FX700 bass is awesome. Great impact, reverberation, and detail. Out of time already? Yep...more later!
NOTE: Please don't read this as the FX700 being bad, it is not and I do like the FX700. Also, I have not yet come to a conclusion!