I think Ninja uses the DT700X - it looks like them anyhow - so they should be good for gaming. (don't hate on me for mentioning him - it's just to say a pro gamer uses studio headphones while gaming)
I have heard of Beyerdynamic sounding bright or harsh but based on reviews of the 700/900, it appears that they don't have that characteristic.
Take my advice with a pinch of salt, as I'm going on what others say on AVForum, lots of reviews and videos I've watched about Beyerdynamic, Hifiman and headphone amps:
If you are looking around the price range of the DT700/900, may I throw a curveball and suggest the planar magnetic Hifiman Sundara?
Hifiman from Lumous Audio, South Africa
www.lumous-audio.co.za
I've also heard good things about the HE400SE for R3k less.
Both of those need a good headphone amp with very low impedance to deliver enough current and power, though.
There is that Schiit stack for sale under the Amps/DAC section that I've seen pairs well with Hifiman.
I got a pair of Oppo PM3, which are entry-level planar magnetic and easy to drive, and the difference is huge compared to driver headphones.
I also game with them every now and then, but mostly use them for music while at work and virtual meetings.
While gaming, everything is crisp and clear.
I'm getting the Zen Dac V2 later this week - my wife won it at the Cape Town Hifi Show last week
I'll post my thoughts on here when I've hooked it up and gave it a listen for a few days, as I'll be replacing my Audient iD4 with it for headphone amp duties as well as DAC between my PC and Mars amp
On a different note, the Zen DAC V2 will only be arriving next week due to a slip up with packing up after the hifi show - they ended up in Joburg with the rest of the equipment
I'll post my thoughts then - looking forward to hooking it up to my amp and using the Oppo's with it.