Sharing mine as well, i'm mining on an 8 year old HP motherboard. It actually only has 1 16x PCIE slot and another 1x PCIE slot. What I did was to add a PCIE extender which allowed me to have an additional 3 PCIE slots. Been using the mobo flawlessly for a few months now.

So from my experience its a NO. You should not see any reductions in hashrate as long as your motherboard can support your GPU.