Nicehash or anyone else, does using CPU lower hashrate with Nvidia cards?

When I use standalone miners I need to put the GPU miner on one thread, and the CPU XMR miner set to use the other threads otherwise the hashrate for the GPU miner suffers which is obviously the most profitable. The new Nicehash miner I seem to have less control, if I just run it telling it to use the CPU and GPU will it adjust making sure CPU doesn't slow the GPU miners?
If not how can I use Nicehash to mine with the GPU's and the CPU without lowering cuda miner hashrates?