so what happened with CUDA magic on ETH?
Amd memory access is better (specially when you can mod memory straps), that why eth is better on amd, core performance is better optimised with cuda (and nvidia have more speed), that why zcash is better on nvidia.
...or should we say, AMD cards have better memory performance under 2GB but have troubles reaching 2GB+ regions. Unless they really going to fix it in their drivers, I'd say overall nvidia has better memory perf.