GL_NV_pixel_data_range

I’ve been looking into using the GL_NV_pixel_data_range extension to accelerate glReadPixels on a GeForce4 4600, using Detonator 40.72. So far I’ve only managed to make glReadPixel performance worse, by playing around with the wglAllocateMemoryNV parameters. Has anyone attempted to use this extension to speed up glReadPixels?