Yes it's fine and with very very little difference.
I'm currently debating upgrading to a GTX 970 4GB 256 bit which calls for a PCI express 3.0 x16 slot. However, I have a relatively old motherboard, an ASUS M4A77D which only has a PCI express 2.0 x16 slot.
I was curious if it was at all possible to actually get the card working without having to buy a new motherboard, and if so would I see any performance problems due to the difference in PCI slots?
Also, as a side question, I'm currently running an AMD Phenom II X4 965 processor. Would I see any significant bottle necking because of the processor?
Impact of PCI-E Speed on Gaming Performance