Bad news for me then. 1GB 4870 are currently unavailable in the store i want to buy my new set. I'm not an enthusiast of extreme performance so I'm thinking of buying single 512MB 4870 for now. In the future I'll probably buy another one.
I even thought about buying 4870X2 and then crossfiring with another one but combining 4 GPUs cause a huge waste of single GPU's power (which is waste of money for me).
crossfiring to a 512mb one would lose 1 gig of usable memory overall as all cards need to match.
And I suppose that this can't be solved in the future. ;(