I am not an expert, but I don't think that there will be any bottleneck with your pci-e slot.
I think that the pci-e bus haven't reached the max yet and that you will be ok with a pci-e2 card in a pci-e1 slot.
I hope this helps.
It's more hype right now than actual performance. Just like when they went from 8x to 16x, from AGP to PCIe. In the future it will be helpful but I haven't seen any benchmarks that would make me think its worth the money right now.