Why does underclocking help?

[xlcus]

Can anyone explain why underclocking the memory on some GPUs actually helps the hash rate?

[kjj]

It doesn't by itself.

The heatsink is built for a certain amount of total heat from the GPU and memory combined.  Reducing the memory speed means less heat from that part, which means more heat removing capacity available for the GPU, which means you can bump the GPU speed up another little bit.

[m4rkiz]

i guess it may have something to do with memory being accessed with as low delays as possible (ie. data can be send and received to\from memory in exact pieces that are needed if you set clocks exactly as needed - no empty cycles when gpu need wait before can acces data or no empty cycles after data write)

but i'm nowhere near any actual knowledge how this century gpus working so don't take my word for it

[w128]

With which GPUs can this effect be observed? I'd expect that it's an effect of the GPUs power/thermal management being able to run the core full-bore without any throttling or trade-offs produced by the memory. Memory clocks are potentially more important for performance than core clock in gaming applications so it wouldn't surprise me if the cards were making core clock sacrifices by default.