So, the demo took 3 1/2 hrs to download, and i instantly got an error after installing, so had to download the 9c x redistribution thing to get it going.
And, much to my surprise, it does play on my machine, and, it plays it rather well too. I just kept it at the default settings it gave me, but it still looks really really good, and is a darn sight smoother than Arma1 ever was. On first impressions (albeit brief ones) the control system is much much better, nowhere near as clunky as Arma 1. The enemy no longer have heat seeking bullets, the maps are excellent and the environment is much more realistic and characterful. There are a few shading bugs, and i'd like to get rid of that motion blur and tone down some of the bloom. But Initial impressions are very favourable.
Matti, you should try the demo. My CPU is an Intel E6300 running at stock 1.86mhz. Dunno how that compares to yours, but although i'm not able to put a number on the FPS, they're easily good enough to play with. My GFX (ATI 4850) was running a tad hot and the fan was kicking in and out, but it's a warm evening with no breeze, so it shouldn't be a problem.
I definitely think the full game is worth getting, and it can only get better from here on in.