do you need surround sound headphones?
if not then studio headphones would definitely sound better (though would require a seperate mic if you needed a microphone) and depending on what soundcard you have may or may not be an option.
the hd598 are phenomenal for gaming. again, they are stereo (not surround) and they have no mic. with a virtual surround (dolby headphone is best) capable soundcard you can make them virtual surround and if you need a mic you could add one to them with either a modmic, clip on mic or boom mic mod.
are they better than the z523? likely clearer highs, however they will not have the same low end kick speakers would have.
as far as headsets are concerned (ones with mic + headphones) i cannot list much for your budget as i dont use gaming headsets myself (i use headphones or speakers)