PCI in the mid 90s didn't mean guaranteed compatibility due to the many different implementations by board manufacturers. Many early boards cascaded the PCI clock off of the FSB using a 1/2 divider, which caused problems if you didn't have a CPU with a 66 MHz bus speed. Early Pentiums from Intel sometimes had a 50 MHz bus speed, and Cyrix had the weird 75 and 83 MHz bus speeds which ran PCI alarmingly out of spec. Early AGP boards had the same problem, but this time ran AGP 1:1 with the FSB, so you could end up with an 83 MHz AGP slot.
I tried my Monster 3d in my core 2 quad a few years ago to try things (tried an original SB Live in there too for the "gaming" port to use old joystick for Earthsiege 1/2) , as far as I can tell besides resolution it works fine.