Here's a little comparison I did of some of the more popular modified drivers. The NGO drivers worked best on my system, though they were pretty close to DNA's drivers in HL2. Below I've included the improvement over the official forceware drivers in parentheses. When Omega gets around to doing a 7x.xx driver I'll add that one to the mix.
HL2 Benchmark
(1024x768, Max Detail, System settings, Heap size 128 Mb)
Hardware OC Coast
Forceware 71.89: 62.8
XG 71.89HD: 62.8
XG 76.41HD: 62.6
DHzer0point 76.44: 61.8
DNA 76.50: 76.4
NGO 76.50: 76.5 (+13.7)
Guru3D demo4
Forceware 71.89: 113.6
XG 71.89HD: 113.5
XG 76.41HD: 113.6
DHzer0point 76.44: 106.5
DNA 76.50: 114.4
NGO 76.50: 114.8 (+1.2)
FarCry Benchmark
(1024x768, Max Detail, Default Shader, Anisotropic filtering ? system, Antialiasing ? system, Renderer ? Direct3D)
PC Games Hardware Demo
Forceware 71.89: 49.94
XG 71.89HD: 50.01
XG 76.41HD: 50.76
DHzer0point 76.44: 50.65
DNA 76.50: 47.92
NGO 76.50: 50.82 (+0.88)
Aquamark 3
Forceware 71.89: 51,530
XG 71.89HD: 51,466
XG 76.41HD: 52,062
DHzer0point 76.44: 51,514
DNA 76.50: 51,658
NGO 76.50: 52,094 (+564)
3DMark05 1.2.0
Forceware 71.89: 3611
XG 71.89HD: 3554
XG 76.41HD: 3599
DHzer0point 76.44: 3582
DNA 76.50: 3617
NGO 76.50: 3675 (+64)