Can those Custom IEMs like JH16/13 beat those top full-sized cans???

There are several other threads discussing this.  My view is that customs and full-size headphones offer totally different presentations, so they're hard to compare.

The best customs are very intimate, with clarity, speed and detail that are probably as good as or better than the best dynamic headphones.  Even the best customs, however, can't present an out-of-head soundstage like a good full-size headphone can.  Full-size headphones tend to be more airy and visceral, offering an experience closer to listening to a live performance than IEMs.  On the other hand, my JH16s give me the sensation that the performance is taking place inside my head, and I'm plugged right into the music.

You also have to factor in comfort for long-term listening--some may prefer one or the other.  Customs are also generally less demanding in terms of source and amps than full-size cans.

I had no direct comparison because I can't afford two high end setups. I had the JH13 and sold because of fit issues, got the LCD-2.

I can say that JH13 has it's minuses and pluses and it can definitely be compared to totl full-size cans. You get the details like no other cans I heard can retrieve though you miss on the soundstage and ambient noises.

The LCD-2 get 90% of the JH13's detail retrieval but is superior in almost any other department. The LCD's bass is the best I heard of any headphone.

HD800's soundstage and openness is better that those two but lack in bass (IMO) which result in a lighter presentation than the JH13 and LCD-2.