I have 6 1070's on a rig with h81 pro btc and g1820. After 15-30min the cpu goes to 100% and the rig becomes unresponsive. Some of the cards start mining with 4-5mh and I start to get rejected shares. I'm using MSI AB to overclock my cards. Task manager reports System, System interrupts, EthDcrMiner64.exe or MSI AB maxing out the cpu.

Use Nvidia Inspector for OC, add Claymore miner to whitelist in Windows Defender.
Close all the apps that are not required in the background, virtual mem set to 20GB+ and give it a try again.