I do such all the time. The cards are "keyed" to keep you from plugging in an incompatible card.
Since no one knows what the old and new cards are, the result will be uncertain.
Bob
I have an older Compaq and want to upgrade the video card . Will the newer 4x or better cards be backwards compatible on the 2x board or will I be wasting power and not see much improvement?
Rob

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic