I have an i5-4590 with a GTX660 powering my DK2. It's failed every benchmark test that's been thrown at it, but it has run everything I've tried on it up to this point. Elite: Dangerous, AC, PCars, all the demos and showcases - no problem.
Some of the higher-end games like Elite and PCars struggle a little bit, but not to the point where it's completely unplayable. There are a lot of people on their forum with the same problems, but way better gear, so I don't think it's all to do with the hardware...
LFS runs like a dream. No lag or judder at all.