There's very little meaningful difference in all open/"semi"-open headphones.
If environment is noisy you're going to hear those noises, with different cans just having different "nuance" in upper mids/treble.
And in quiet environment if there's someone close to you he's going to hear a bit, though at hearing safe volumes that sound simply won't carry far.
http://graphs.headphone.com/index.php?graphID[0]=4163&graphID[1]=2141&graphID[2]=&graphID[3]=&scale=30&graphType=6&buttonSelection=Update+Graph
In binaural gaming (or movies) DT990's treble isn't really problem (also
K712 has some bump in treble) and neither are mids.
In fact binaural sound seems to like little more distant and analyzing mids instead of more pushy ones.
This is what MLE says about so hyped HD650 in thread's start:
The DT990 destroys the HD650 in both depth and width. So how's the air within the soundstage? Well, the problem with the HD650, is that it's a very full sounding headphone. Thick, warm tone tends to make the soundstage seems less airy and smaller...
Positioning and soundstage tend to go hand in hand, so if the soundstage isn't great, the positional cues will suffer. How did the HD650 fare positional-wise? Well, they were good. Not great, and could obviously be better, but they do their job.
Does that sound good for HD650's sound signature/type, if it takes heavy beating from DT990 in both soundstage and positioning?
K712 with even bigger soundstage wins DT990 in competitiveness.
Again DT990 has edge in bass immersion.
That would be pretty good summary between them.
If you have nearby some shop with DT880/990 and K700-serie AKGs that could tell how their comfort feels to you.
IMO DT990 has edge in comfort with less feel of pressure.