My MX4000 is slow in NFS4/5 in NFS3 it's OK, but Nfx4/5 is only about 20fps. this could be due to the 32Bit Memory Interface a 64MB MX4000 PCI has.
I think the 128MB models have 64Bit memory interface.

The D3D Setup on NFS 3/4 does not detect the MX4000 correct, it always says "software" rendering. You can activate D3D Device 1.