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ATi GPU FAQ
Which video card? If you have a G80 core onwards (or the ATi equivilent) you'll do better with the GPU client, if your GPU isn't supported then I'd drop the graphical client and go for two instances of the "No nonsense console client" to boost output. The only real way to boost the cpu clients is allowing 100% cpu/memory and overclock.
With the GPU client raise your shaders clock to improve output, check that it is stable though, my GTX is 1849 and the GTS is 1750, you'll get EUE (Early Unit Ends) if it is not stable.