I was curious about the same thing. It's hard not to be a bit paranoid considering there have only been eight reviews on Amazon over the last year, and at least three of those are from patrons of the same gaming clan website, where coincidentally, E.D.G.E's Rich Heimlich (who's also a member of this site) led (maybe still leads) the GRAW2 division.
Paranoia aside, the GX400's seem to be ER4P's with longer cords and a microphone. At ten bucks more than the 4P's, you can't go but so wrong.
I have a set of Sony MDRF1's and Sennheiser HD580's. I'd just use those, but I simply can't wear headphones for an extended period of time. In both cases, an hour or so of gaming or half hour of music, and I'm tugging on the cups without even realizing it. At the same time, I can listen to a thirty dollar set of Sony earphones all day without even realizing they're on. So, I think I'm going to give them a shot. Worst that can happen is they turn into another gadget forgotten in the junk drawer.