I've been using nothing but nvidia since the 6000 series and I'm fairly certain you don't get performance improvements 6 months after the release of a new generation. Maybe for SLI, but for single cards setup I've never noticed anything. Which is ok, it just means we get proper support asap, not 2 years after we buy the card.
Except in this case all of Gen6 is very similar architecture, so they all will likely benefit from enhancements to the driver. They're all on DDR3, they all use very similar CUDA cores.