I haven't heard the GS-1000s, but I've got RS-1s and PS-500s on loan, and I've listened to the PS-1000s several times with the same gear (24-Bit AIFF from a Macbook Pro with an Audioquest Dragonfly)
The RS1s and PS500s are really quite similar. The PS500s has a much more extended bass with more slam, and perhaps a smoother treble. But the "resolving power" is excellent on both, and there have been times I forgot which one I was wearing.
The PS1000s still have a strong family resemblance. Very powerful bass--haven't compared them to the PS500s yet--with lots of slam and extension. The different cup/pad configuration makes for a different presentation. It's a little more "distant"--Row F instead of up on the stage--and there seems to be more "air." It doesn't strike me as being 'better" so much as "different." The PS1000s are very heavy, although they were comfortable for me, your mileage may vary. I could be very happy with either of these.
Both of the PS500s and the RS1is work beautifully with a wide variety of material, from Hendrix to Arvo Part, Diana Krall to Wilco. Listening to Cowboy Junkies right now.
I think that these two models represent a kind of second value sweet spot in the line, getting a lot of the sound of the $1,000+ headphones for closer to half that.
Good luck and if you have any interest I can listen to the PS1000s at more length.