Sorry can't provide any resources right now. If you search a bit I'm sure you'll find some latency comparisons between DDR and GDDR.
But basically GPU memory (GDDR5/6/6X/etc) is optimized for bandwidth (because GPUs need to move a lot of data, have few branches, few unknown data dependencies, high spatial locality). CPU memory is more optimized for latency (because of branchy code).
But basically GPU memory (GDDR5/6/6X/etc) is optimized for bandwidth (because GPUs need to move a lot of data, have few branches, few unknown data dependencies, high spatial locality). CPU memory is more optimized for latency (because of branchy code).