Same here.
Odd how some people have this issue with 4K/Quality and some don't. I'd be tempted to try a re-install but I doubt if that would fix it. I remember a previous update which had frame-rate issues, in the end that was network-related at Frontier's end. Maybe try a hard-wired connection to your X, if you're not using one already.
I did a re-install of ED and have a wired connection, I also placed my One X in the dmz so all ports are open, my connection is rather good.
The performance dip is quite intermittend though, it can happen that when I'm in station with quite some traffic that the game runs smooth and while I'm a couple thousand lightyears outside the bubble in a system with only a star present and it stutters, or vice versa.
Quite often I see a performance drop when I'm in FSS mode and move the reticle over a group of bodies, that doesn't bother me realy but to me it confirms that it's probably not a hdd issue.