How does either compare to the HD 700 though, this is going to be primarily used for gaming and I heard the HD 800 series is picky about the audio quality. Is the difference as big as the price tag?
Both 800 and 800S are picky about audio quality but the 800 more so than the 800S, but for gaming it really doesn't matter since its all digitally generated audio unlike music which comes mostly from analogue instruments. While I don't game much these days the HD-700 with a STX sound card was pretty good to me, great positional audio and one of the most comfortable headphones. I never really used my 800 for gaming since it didn't sound as good as the HD-700 from the STX, I've since sold the STX and my gaming is limited to 1 or 2 days a month of old games like Test Drive Unlimited 1/2, Metro 2033, Tom Clancy's HAWK, Crysis, COD: World at War, Tomb Raider: Underworld, Anniversary and Legend. My gaming rig is old and I just leave it as is on Win7 (has win10 digital key), audio is now optical to Teac AH-01 and either Stax SRD-34, SR-225i (modded) or HE-400 (modded), HD-700 only for music these days.
The difference between the HD-700 and HD-800S is not as big a difference in the price tag if using both for gaming, for music it depends on the individual, for me the difference is not worth the price difference at this time, maybe when the 800S comes down to $1000-1100 since the 800 is usually under $1k these days.