Does PCIe 2.0 bottleneck GPU performance

[harryface]

I have recently upgraded my GPU to a EVGA 980 SC and am currently using it the 16x port of Asus P8Z68-M PRO. I think my stock 2500k is probably holding my pc back the most.

 

[harryface]

Overclock it.

I've had a go a few times, but I don’t have any experience doing it. And every time I seem to try its really unstable. Constant blue screens.