I dropped triple compressed cobble into the smeltery. It melts just as fast as cobble, but obviously contains way more. I made my smeltery pretty tall. Also, use a liquid transfer node with a couple of speed upgrades on a drain straight to your QDS. I run a server so I chunkloaded the area once it was full of triple compressed cobble. Ran relatively quick at that point.
thx for that tip. i didnt try that, cause in earlier versions, you couldnt melt down compressed cobble.