This Nubus card (the 4 8 and the 8 24 are same thing, it is just that the addition of two 256k vram simms makes the 4 8 into an 8 24) is currently on eBay. It is an unaccelerated 640x480 card, I think, and so it is of limited interest, but it has the ability to work in tandem with the 8 24 GC card for accelerated video across more than one Nubus slot. The particular magic involved is called Nubus block transfer. There is an Apple TIL article about it, dealing with these "three" video cards in particular.
I happen to have a IIfx and an 8 24 GC card, and am wondering about putting a bid on this other card to work with it, just for kicks. Before I spend more money on scrap electronics, however, can anyone tell me this: Is this feature (Nubus block transfer) something unique to a small range of Apple cards or would it be available on most any late-issue Nubus video card? I do have others to play with already.