UPDATE: I managed to get the game running very smooth by defraging game cache files (in steam, right click on CLIFFS/properties/local files/ then defrag cache game files) + tuning up my nvidia control panel settings (Texture filtering - from quality to High performance and Power management was earlier on Prefer maximum performance). Also I tuned a bit my ingame video settings and here they are:



Game still looks good and while Im waiting for more optimisations (mostly for land objects) from devs this would be OK for now...it runs great...

Also, from day one Im using MSI Afterburner for overclocking my MSI GTX470 Twinfrozr2 (Oc on core 750Mhz) and in BIOS Ive raised my CPU (i7 920) from 2.66 to 3.5Ghz with HT set to OFF).
For fine tuning win7 (64bit) Im using Yamicsoft Win7 manager where I can fine tune the memory usage, registry cleaning and defraging, pagefiles, win processes, SATA speedups etc etc). Although Gamebooster will do the job quite well.
For defraging my HDD Im using excellent (and free) Mydefrag utility. Highly recommended.