Thanks mate
All common cards are supported. 75-86mm diagonal is the most used dimension for all high-end and midrange cards.
I measured a huge amount of cards:
nVidia:
GeForce 68xx
GeForce 78xx,
GeForce 79xx,
GeForce 8800 (G80 and G92),
GeForce 9800 Series,
GeForce GTX2xx,
GeForce GTX4xx,
GeForce GTX5xx,
GeForce GTX6xx
ATI:
HD 38xx,
HD 48xx,
HD 58xx,
HD 68xx,
HD 69xx,
HD 78xx
HD 79xx
All of them have a diagonal mounting dimension between 75 and 86mm. There are only few exceptions which are smaller like HD 2900 series and of course the dual GPU cards like HD4870X2, 9800GX2, 7950X2, GTX295, GTX590... These are not supported.
Also a lot of low end cards like GeForce 8600 GT have a mounting dimension of 75mm diagonal. I just can't guarantee them all because there are too many custom PCBs out there.
But just measure the cards you got out there and you'll see the pot will fit on almost every card