1.6.4 can produce compute errors on BC drivers, maybe you have a ton of those? That is why i recommend 18.3.4 or18.6.1 on the first page, it works a lot better on those drivers. Maybe if you can try it on one of those?
Everything has been rock solid on the blockchain drivers. I'm not going to turn these systems upside down ATM to 'test'. Whatever you have done to try to squeeze more hash out of the cards was not done in testing the Blockchain driver. After a long time SRBMiner user, I guess I'll switch to XMR-Stack if the blockchain drivers are suddenly not being supported?
Like windows xp, old things get abandoned after some time in favor of newer. 18.3.4 are great drivers, stable (and not really new also).
Ask livada, he also never wanted to stop using blockchain drivers, and finally when he gave up and tested these two drivers, he said he got more hash, more stable system and lower power consumption.
So i will leave it to you, it's your choice.