£75 yes definetely for gaming you won't find a better gaming headphone unless you buy AKG Q701, K702, etc. They were £115 in the sale a few days ago.
If i had the option between the 2 I would have went for the K702 for £115.
If i were to compare the 2 the K702 is a 9.5/10 in terms of gaming the HD598 would be a 9/10.
Compare that to some gimmicky headset by steelseries or razer, etc I would rate them as being around 6/10 for gaming.
For movies you will want something with more energy and bass.
Good gaming headphones don't make good movie headphones. In competitive gaming you don't want to hear loud blaring explosions you want to pinpoint soft foot steps. Whereas in a movie you want to feel the explosion.
So there is no such thing as a great competitive gaming and movie headphone.
If you want a great immersive headphone which is brilliant for movies then look at phillips fidelio x1 in the members market or brand new fidelio x2 (newer model with removable ear cups)