Is anyone else having some real trouble to properly run this game? I can barely play it on medium, and my rig is way ahead of the minimum requirements.

Are there any .ini tweaks or fixes to help me?

My specs:

GeForce GTX550ti 2743mb (with the latest drivers)
Intel i5 3330 (4 CPUs) @ 3.2ghz
4gb RAM
Windows 7 HB 64bit

Some settings make more of a difference than others. To play at a decent frame rate, I had to:
disable Antialiasing
disable SSAO
disable Mirrors
disable Anisotropic filtering
reduce post processing to medium
reduce foliage to high

The first three make the biggest difference. I didn't notice much loss in visual quality, but the frame rates improved a lot.

I have nearly the same system as you, although I swapped out my GPU for a new one and I have 8GB RAM. Much what hudfreegamer posted works, or you can use the preset High which works nice. I had Anti Aliasing turned off and ran at 1920 x 1080 with reasonable framerates.