The PSU looks same, but you said the PC does not have the bsod since you used the gtx760 in other pcie slot. That means the gtx760 may have the issue with the 1st pcie slot.
Next you may try to update the amd chipset driver
http://support.amd.com/en-us/download/chipset?os=Windows%208%20-%2032 after that try put back to the 1st slot to see the pc works fine w/o bsod or not, if the pc still get the bsod, then if you want try the BIOS update, but if you don't feel comfortable to do it, and just use the 2nd slot. Event it runs at x8, you will be fine because you will get the same performance, and the disadvantage is that you can't use two GPUs.
Review: Impact of PCI-E Speed on Gaming Performance http://www.pugetsystems.com/labs/articles/Impact-of-PCI-E-Speed-on-Gaming-Performance-518/
Because you don't have other GPU or PSU to try, how about your friend? Because if you don't have other GPU or PSU to try you hard to know where the problem comes from. There are the possibilities like 1) GPU, MB, or PSU has problem, if the pc got bosd even you try to use 1st and 2nd pcie slot. 2) MB has problem, if the pc got bsod only the GPU in the 1st pcie slot.
One more which model is the gtx760? oc version or regular one? If it is the factory OC, you may try use the msi afterburner to under clock or increase the voltage a little bit, and that will help.
msi afterburner
http://event.msi.com/vga/afterburner/download.htm