I tried them and they seemed slightly slower in Unreal and Serious Sam but slightly faster in Quake3. Also until the refresh rate fixes are updated all drivers above the 2742s are stuck at 60 Hz in Windows 2000/XP.
The 27.XX drivers greatly improve D3D performance, especially on DX8 games. Check out my 3DMark2001 score...
3DMark is not a game nor does it translate into real world performance in any way. Do you have some real game benchmarks that showed a performance boost?