Core Temperature Range

So I recently put together my first PC and want to make sure it's not overheating. Here are the current specs:

Processor: AMD Phenom II x4 965 Black Edition
V Card: Radeon 6870
PSU: Corsair 750
Case: Antec ATX Mid Tower

I peaked in my running temps last night when I played SC II (which came as a surprise. I think it had to do with a download update). My cores looked like this:
Core 1: 56 C
Core 2: 55 C
Core 3: 55 C
Core 4: 56 C

That is the hottest that they have ever gotten. I've played hours of D3 and they only got to 51 C. (The vcard gets up to 65 C).

The case is constructed with the PSU on bottom, then the vcard, with the cpu at top. There is a front fan, a top back exit fan, and a top "ceiling" exit fan. Of course there is a fan on the stock heatsink and psu. I also have one more front fan but not enough slots on my mobo to plug it in. I'm thinking of getting an adapter to plug it into the psu. (I've heard those exist?)

So basically, how am I doing? Is it too hot? I started to really worry when it broke 51, which is the usual. Any help would be fantastic!