To answer your questions, I really don't know. But, I would suspect the +4 pin will supply more power to the motherboard. The 20 pin will supply enough power for it to run but not quite as much as it should have. I would not worry too much about any damage to the board. The GPU gets most of it's power from the pcie conntections, but the extra 4 pins may help. As far as the memory, I would suggest running memtest86
to test the memory. The link is to a tutorial on how to run it. You are looking for bad ram sticks or defective dimm slots.