PCIE video cards and DRI

[Jack Howarth]

    Does anyone know if DRI is fully enabled under the latest
Nvidia and ATI closed source drivers when used with PCI-Express
cards. I have set up a number of Linux boxes with Nvidia and ATI
AGP cards and DRI has always accelerated nicely. However I can
find little information on the web concerning how well DRI and
PCIE play together. In particular, are there any limitations to
DRI support of PCI-E currently that would severely degrade the
performance of opengl. For example, the ATI fglrx drivers on
a Radeon 9600-XT improve in glxgears frame rate from 200 to 2000 fps
upon loading the fglrx kernel module. Will a similiar performance
improvements be possible with DRI on PCI-E cards? Thanks in 
advance for any advice since I don't want to get stuck with
horrible graphics performance under Linux just because DRI is
AGP-centric.
             Jack