Metal shield would help depends on how you mount the gpu, if you let the riser (screwed) carry the gpu then it might help.

Voltage might be good, when there are minor burns in wire the gpu can't pull more power and less hashes (if the system didn't hang)..i think, amps is a lot better indicator than voltage.

If caps backs each other, like if 6 out of 10 is working and 4 are bad, the riser still works, then more is better. I think it acts as electrical noise filters.

Led lights should indicate some thing like gpu is unplugged/loose, riser is powered off (12v power not connected), and usb cable not connected.

Makes troubleshooting a lot easier.

I got an old motherboard i'm stil using circa 2007 or 2008. There are four led lights, if they lit all green then i knew checking on the rig is by remote login, if not then i might need to plug the monitor to check what's up.