I've just signed up to answer this - recently bought a Gigabyte RX 5700 XT OC for a good price in order to mining with it and I get exactly the same memory temperatures under mining load with this card when running the default fan profile of the card. I can get the temps down to 96 degrees if I raise the fan profile up to 80% (which keeps the core temp (non-junction) at around 58 degrees. Having done a fair amount of research on the subject through various forums and articles, it does seem as though this is standard behaviour for these cards when mining or performing memory intensive workloads, regardless of the model, and that the memory temperature is a 'junction temp', not the edge temp. I've noticed that under more normal gaming loads the temps get up to 80 degrees or so with the standard fan profile so it does seem to be the mining that really pushes it higher.

Having owned a number of other graphics cards I still think these temperatures are too high versus what I'm used to seeing normally but maybe the true junction temperatures in other cards aren't reported in the way that they should be. What rx 5700 xt models are other people mining with?