Here is my 955 overclocked to 4.0 GHz with a CM 212 EVO (full specs below) after about 10 minutes of the AIDA64 stress test,
and it idles around 26-28°C with a room temperature of 23°C.
If you're idling at 50°C then I would be looking at what kind of airflow you're getting through the case, adding a second fan to the heatsink or changing the thermal paste isn't going to lower it by much if the airflow isn't there to begin with. Also what kind of room temps is the computer being run in?
P.S. Have a link to the case you're using? What you have listed isn't much to go on.
P.P.S. To give an idea as to how much the case and what it has for airflow can do for cooling, I just recently changed my case from an Antec Sonata III to the Antec Three Hundred and both idle and load temps went down by ~10°C (same with my video card). I also added a 120 mm 1300 RPM PWM fan to the back and moved the fan that came with the case (Antec TriCool) to the front, and left the other two fan mounts (one more on the front and one on the side) empty for now. Not only did all the temps go down, but now when gaming I can barely here the fan on my video card where in the old case it tended to get rather loud.