pci-e 2.0 is version and 1 mean that you are able to run one card at full speed like 1 x16 so its mean there is only one slot available for full speed.
Correct me if i'am wrong but you're saying that a 6870 for example which is sold as a 2.1 only can run at full speed, standing alone or just has one slot ??? What are you talking about ?????