Some variables to consider :

- Video card internal bandwidth (EDIT: video RAM clock speed, type and bus width)
- PCI vs AGP bandwidth (AGP cards typically run at AGP 1x when initialized by BIOS, AFAICR, which is equivalent to 32-bit PCI at 66MHz , whereas PCI ones are 32-bit at 33MHz on most consumer boards . Someone will surely correct me if this is inaccurate)
- quality of VBE (VESA BIOS Extensions) implementation by a chipset OEM or in the TSR (OEM or third party) being used and whether an LFB is implemented (Linear Frame Buffer)
- Whether write-combing is enabled or not .

EDIT : See also PCI Video cards benchmark: Electric Boogaloo Edition

thanks darry, what you wrote was very helpful and makes a lot of sense in fact!
also thank you for the link, really interesting and helpful for what I'm doing

cheers