Allow me to interject.
The 2X / 4X / 8X was taken from the back of the FX5200 AGP box. I would be happy to send you an image of it if you would like.
It is my understanding (as we do not remember if we tried this lately) that this and other cards like it will run in a 2X board, just not nearly like they should. It would be good to note, The cards listed at the site posted above hpcompatible.com and at this address:
(same site different domain name)
Are advertised primarily as they are Half Height or Low Profile Video Graphics cards. Both AGP and PCI even PCI-Epress. All of these cards come with both the full height ATX bracket and the Short Low profile (3 inch) brackets.
It is our understanding that yes it will function, just not as it should and not nearly as fast as it could.
We would be happy to dig out a 2X MOBO and set up a system just to test the theory, if you think anyone could benefit from that let us know and we will.
Hope that helped.