"I have massive slowdown when scrolling"
That's the problem mate. Your comp is fine. The code is "fine". I quote it cause actually is horrid and full of bugs but it's not a poor graphic implementation what is causing your problem.
I had the exact same problem with a very good computer. Tried EVERYTHING, and it didn't work. In the end I just bought a crappy mouse and the scrolling slowdown just dissapeared and everything works fine. If you're desperate to play like me, try plugin in a crapmouse that you have around.
In case anyone wonders, I don't post in the cursor bug/lag the solving of my problem cause is NOT solved. I had to spend money and buy another mouse, and the fault was not my mouse cause we're a legion with this bug, only some of us didn't manage to identify the cause and we relate it to graphics coding or another things. It took me some time to realise that it was scrolling, and certain way of doing it, what caused the bug.
Please developers, make your best to make the game compatible with mouses or drivers or whatever it is that makes it so impossible to play! I've been asking on the chat and there are a few persons other than me that are experimenting it!