This is my first time mining so I thought it's best to begin learning small before building a full 7gpu rig. I started with putting two rx570 cards directly into my old pc's pcie-16 ports without any riser. I bios modded them and overclocked both and got pretty decent speeds. When I run the system with only one card I can get about 29MH/s on my Gigabyte Aorus and 26-27MH/s on my Msi armor. When I run the system with both cards, my armor card drops down to about 19Mh/s. I've tried everything but I can't find a solution, could someone help me out?. These results I got using Claymore mining ethereum.