Question on AGP 8x cards

I’ve seen a number of 8x agp cards coming out on the market. Do they require a motherboard with AGP 8x support or do they down grade to 4x?
I noticed intel does not make an 8x agp slot motherboard yet. So what can you hardware folks tell me about the 8x cards other than don’t bother with them? I also read the cards take different voltages is that because the 8x runs a fan and heat sink from the card? I’ve already looked at Tom’s hardware for info and ati.
Thanks