I'll preface this by saying I don't fall into the benchmark trap. They're too easy to manipulate (all of them), and numbers don't mean as much to me as real-life usage. That doesn't mean they are useless though, they can give an idea of what to expect when watching them being ran on a phone you've never used, and in a case like this where the hardware is identical, Quadrant is a very good indicator of how software affects performance. Or doesn't affect it.
On the left is the T-Mobile G2X, and on the right is the LG Optimus 2X. Two phones with the same specs, but very different software. Both phones have a Tegra 2 at 1GHz, 512 MB of RAM, and possibly the best LCD displays you've ever seen. The hardware is identical, but that's where the similarity ends. The G2X runs stock Froyo, while the Optimus 2X runs a very skinned version of Froyo. While using these two, I'm not seeing any performance difference, so I decided to let the benchmark be the judge. Watch the video, and dissect the scores, after the break.
The T-Mobile G2X is on the left, the LG Optimus 2X on the right