click here for a card I recently fitted in a home build to upgrade the onboard graphics. It has passive cooling, so no fans to add to the noise. As a general user, occasional low tech games. It does everything I require of it. I'm sure Doom 3 would make it curl up its toes and expire, but as far as I'm concerned this isn't a problem.
8X cards will work in a 4X slot, but only at the lower speed. The performance difference however isn't 2 to 1, the performance loss is only marginal.