ITReviewed posted a review on the AMD Phenom II X2 550 Black Edition. Here's a bit;

Targeted at the enthusiast crowd – hence its Black Edition moniker – the Phenom II X2 550 Black Edition (from £68.70/$99.99) runs at 3.1GHz. This makes of it the second fastest Phenom II on the market. The speed crown goes to the Phenom II X4 Quad Core 955 Black Edition, running at 3.2GHz (around £162/$254). Furthermore, for under a mere £100 you get an unlocked processor. So what does that actually mean? Well, since the Phenom II X2 550 is a Black Edition, it lets you play with the multipliers in your system's BIOS. You can also crank up memory speed to 1600MHz, which previous Phenom IIs also had no difficulty in handling, increase the base clock and increase the integrated memory controller and the HyperTransport multiplier. With careful tweaking you can overclock the processor somewhere between 3.8GHz and 3.9GHz, which is outstanding.

The latest Phenom II X2 550 Black Edition is the first dual-core Phenom II chip. And it's great for gaming and multitasking. The 3.1GHz processor performs very much on par with Intel's 3GHz dual-core E8400, but costs £50 or so less. Furthermore, for the reduced price you're getting an unlocked processor to play with. The downside is that power consumption is a tad high for a dual-core processor. On the flipside a complete AMD-based system is much more energy efficient than an Intel-based rig. The Phenom II X2 550 Black Edition is an awesome budget processor for enthusiasts - if only it could roll over the 4GHz barrier! It's not the most powerful at running heavy workloads - that's what quad cores are for - but for general computing duties and gaming it's an outstanding buy.