If you're getting HW then you're pushing your GPU too hard. Anything above 0 isn't acceptable.
No, I have a couple that throw errors at stock clocks and low intensity, whereas 90% of my GPUs stick at 0 with the same config. Imperfect silicon, I guess. But mathematically, 10 errors a day have no tangible effect on performance, so it's not worth worrying about until the errors accelerate. WU is the same for the problem cards as the rest, in other words.