To answer the question correctly.
The 3850 is almost twice as fast as the X1950PRO. and the 3850 has a special feature known as Power play meaning the GPU will run at 300MHz while running 2D applications but as soon as the GPU is taxed such as in a 3D applications, the GPU speed will jump from 300MHz to 668MHz.
Please note: The AGP version of the 3850 doesn't support Power play, so it runs at 668MHz all the time. I found this out the hard way. I own 1 3850PCI-E, 1 3850 AGP, 1 X1950PRO AGP. 1 X1950PRO PCI-E and 1 Geforce 7800GS OC AGP.