The driver support for the 5500 4GBs just seems horrible. Haven't ran enough tests, but it fails miserably at allocating a large portion of the available vram. Most 8GB gpus have a limit at 7.75GB, i.e. 256MB is reserved. It feels like this might have leaked over to the 5500 4GBs as well, but I'm just guessing.That said, afaik I don't think anyone is able to mine the current ETH epoch (379) with their 5500 4GBs.