Okay. I have had this game since launch and have enjoyed it many times.
At the start of the year I installed it from the disk and it was unplayable.
At the menu screen as the menus move about the whole thing stops moving and then very very jerkily gradually starts moving but takes much much longer than it should, jumping about all over the place.
In game it's fine until you open a blueprint when the entire game shudders to a halt.

So i got the GOG version as soon as I saw it was out hoping it had been optimised but no luck the same problems.

Anyone else have this and even know what I'm talking about.
More to the point, any fix?

I've been looking forward to replaying this for soooo long!

Have you tried changing the renderer from Hardware to Software? I had the same issue on the retail copy, and doing that cleared up most things. The game seems to run (and look) just as well using software, so I don't think it's much of a sacrifice.