CPU Heatsink upgrade help

Hi everyone. Just looking for some help in upgrading my CPU Heatsink. Google hasn't been much help.

Here's my setup:

Case: HAF 932
MB: GA-990FXA-UD7
CPU: AMD Phenom II 965 3.40Ghz
RAM: OCZ 4GB Kit (2x2GB) DDR3 1600Mhz
PSU: Corsair HX750
VGA: Gigabyte Radeon HD6950

So, I'm pretty sure that covers that.

I'm looking to get a new heatsink as the current one is stock and it's pretty damn loud and doesn't appear to work very well as when I've only a couple programs running, the temperature is around 55-65c (131-149f) which I'm pretty darn sure isn't good.

I'm fairly competent in computers but I've never really dabbled in Heatsinks. I was looking at getting a Noctua NH-C12P-SE14. Then I found out it's apparently not aiming at full tower PCs (One review I read) and also it's a tad more complicated to install?

So I started considering the Noctua NH-D14 but then I finally noticed the size and that it can have some issues with RAM and whatnot.

I was hoping for someone to advise me on whether it would actually fit in my system (I don't have anything to measure the size but the heatsink looks like it wouldn't have enough space, but then I have no idea if I'm judging it correctly) or if there's a better option.