^^^ That should be stable/error free for you, yes they will hash @29mh/s but will probably crash after a few days. That one card you had going at 29 was probably stuck at a higher frequency for a bit then got reset with a reboot.
Ok! I had another problem which is sometimes GPUx hang in openCL and claymore restart itself. Normally when this happened, it will loop within 3min until computer totally hang and just stuck there without restart anything. I tried many drivers, reinstall windows10, update claymore version, change riser, it solve nothing