Yeah, got to chime in as someone who is also having performance issues of the likes there have never been before.
The game starts out just fine - no lag, no stutter, everything's running silky smooth - as expected when there is little of anything on the map, I imagine.
My game is currently approaching year 2400 (800 systems map) and it has been becoming increasingly painful to play. On normal speed, days still progress at roughly 1 day per second, but there are micro-freezes happening every 5-6 days or so (only a split second or so, but it's annoying as all hell - and forget about space combat looking good), menus respond with considerable input lag and panning the map on galaxy view makes the game stutter like hell. Once every month or two the game freezes up for ~ 5 seconds before moving on.
Note that I am playing a multiplayer game with my friend, and he is experiencing the same issues (we both tried hosting the save, makes no difference to the performance). We had to stop playing last night because it frankly became too frustrating to deal with, and that's with neither of us being involved in any wars at the moment, where we were basically both sitting in place, trying to pan the map as little as possible and just building stuff up while cursing at slow-to-respond menus.
I dread to imagine how that game is going to look 50 years down the road, much less having to manage fleets and invasions and what not with the horrible stutters and micro-freezes and menu lag. We tried both the current patch and the beta patch, which made not a lick of difference for either of us. Something is obviously very, very wonky here as the game becomes increasingly unplayable past the early midgame, and that's on an 800-size map!