Our test system consists of an Asus A8N-SLI x16 motherboard, a 2.6GHz AMD Athlon 64 FX-57 and 2GBs of memory.
The scores we got from our card were very good. The tests I ran showed me that the modified card has the drop on the more expensive GeForce 6800 GS in most cases. Far Cry is a good example, with the GTO² besting the GS by a healthy 16.8fps at 1600 x 1200 with 4x FSAA and 8x AF. The lead in Half-Life 2 was even more pronounced with the modded and overclocked card hitting almost double the GS. However, Nvidia does have strong points. While the HDR in Day of Defeat: Source is designed to work with either Shader Model 2 or 3, it is faster on Nvidia, with the GS keeping up with the X850. Also, OpenGL has always been Nvidia's strong suit, and the GS matches the Sapphire card. The X850 doesn't lose, however, and that's an important point.
One feature that the GS does have that the Sapphire doesn't is Shader Model 3 support, but you have to ask yourself how likely you are to run in that mode with a card such as the GS, when really you'd want something faster.
The Sapphire Radeon X800GTO² is great news then for bargain hunters. It means that £150 and a little bit of work will buy you a very fast graphics card. Of course spending £20 or so extra will net you a 6800 GS or a X850 XT, but in most situations the modded Sapphire X800GTO² will outperform them both.
For those in the know this is the best worst-kept secret in the graphics market right now. Since the price of X850 XTs has come down, it's not quite the bargain it once might have been, but it's still great value. If £150 is the kind of money you want to spend, this is a card worth hunting down.