the zotac amp edition i do not recommend as the cooler is a 3 slot size (huge) may prevent sli on certain motherboard configurations
thanks i didnt know that
physically you're going to have 6GB GDDR5 with 2 GTX580 3GB. but each of the GTX580 are going to use their own on board VRAM and will not somehow share the VRAM between the core. for example if the game use 1gb VRAM the 1st gpu will use 1GB of it's VRAM and the 2nd also will use 1GB from it's own VRAM (maybe this is not the exact way how they are going to work but i think this is the easiest way to understand it). that's why in CF or SLI 1GB + 1GB = 1GB not 2GB. this is one of the limitation from using SLI or CF. having both card or triple card work in tandem will give you more processing power due to more core available which means more performance but in real games the actual performance performance will not always double or triple because of the scaling.
thanks u cleared up my confusion some