Hi, well I think I got it sorted.
Wasn't drivers as I keep those updated from NVidia, as well as the GeForce experience extensions.
I moved back to 1.8.4 and all stable, added optifine and still everything is stable.
Tried reloading 1.8.7 from fresh (purged the old profiles and associated files) and the problem returns. Optifine makes no difference.
So touchwood 1.8.4 w/optifine is stable.
Lets hope Mojang/Microsoft get this bug fixed soon.
Rogue