That's a difficult question to answer correctly. Not only because of the multitude of hardware differences between GPUs, but also because GPUs have a different

That's a difficult question to answer correctly. Not only because of the multitude of hardware differences between GPUs, but also because GPUs have a different strategy of latency-hiding than CPUs. ... And if you can successfully "hide the latency", then you kind of don't care about the latency... I'd estimate CPU RAM latency to be 50ns to 100ns and GPU vRAM latency to be 100ns to 500ns, depending on architecture. (There's many more GPU architectures out there, and they all have very different latency characteristics) But again, GPUs "don't care" about the latency to some extent due to their massive number of concurrent wavefronts/blocks. While CPUs also "don't care" because of L1/L2/L3 cache and out-of-order execution. Its probably more important to understand the different strategies of latency-hiding between CPU vs GPU, rather than knowing the actual latency figure.