Am I doing it wrong?
what GPU/CPU do you use?
the cuda-client is still experimental and sadly burns the CPU by ~50% (on a dual-core)
and at the same time only loads the GPU to 50%.
that's why i usually don't use the cpu-client on the same machine,
but i just tried and it gets ~1000khash/s, like on my other machine per core too,
and it doesnt really slow down the cuda-miner, it still gets it's <18M.
it's more efficient though (at least on my config) to start a second cuda-client,
results in 100% CPU, ~70% GPU load and a few more Mhashes (<18M single, 2x~13M 2 instances).
but everything will be even more sluggish.