From what I have seen, it appears that the graphics card isn't a standard PCI-e, but rather it's an MXM card with a custom cooling enclosure. I don't know if you can buy the enclosure from HP's parts warehouse without getting the card, but if you bought one with a graphics card, you should be able to upgrade it to another MXM card. They do show a video on how to upgrade the MXM card inside the enclosure on HP's site. From my (admittedly limited) knowledge of graphics cards, there seem to be a lot of MXM cards. nVidia's Quadro for instance goes up to 5000M (but their highest performing card is 6000, which does not appear to be available in MXM format). There may be some other differences between the PCIe and the MXM cards too (clock speeds, etc.) that I don't know. Having said all this: I do not own an HP Z1 (yet), and I have heard of no reports of people swapping the graphics card for another model not specifically endorsed by HP.