a bit of necro here but... 558/598 at their price point are the best headphones soundstage wise for fps games, if you are willing to pay more however AD700X, K701, K702 and Q701 are most certainly the very best headphones for fps gaming whatsoever.
since most people caring about soundstage in fps games etc are people who play CSGO, as there isn't really much other main-fps competitive games currently played at toppest of levels, i can tell you that it won't matter much between something such as hyperx cloud or even ****ty siberia headsets and K701 due to CSGO's sound being completely ****, just choose whatever you want that has some good soundstage, HD 600 works great aswell, not as good as other but it doesn't matter at all in CSGO, I use HD 600 myself