Does Stability/Overclocking Affects Current Effective Hashrate and Stale Shares?

Hi guys,

I am pretty new to mining and have a rig that mines at around 320mh/s (green line).

I notice my current effective hashrate (blue line) in ethmine.org varies widly. It can drop as low as 260mh or even exceeds 320mh (hos is that possible??). The average (orange line) is reported to be 301mh/s.

I did some tweaking and BIOS flashing on my RX580 and they are mining at around 29.4mh/s. I am not trying to push them too much in case of instability.

However, I am wondering if the overclocking resulted in the crazy looking blue line? Could it be that I overclock the cards too much and it caused them to become unstable and hence affecting the blue lines. I checked the rejected shares in claymore and they are around 2-3 for every ~5K accepted ones. My stale shares are very high though. Around 8-12%. I am not sure if its due to rig stability.

I tried claymore 10.0 to latest 10.6 and different versions of drivers. Don't needs to change anything. I did lower my clocks from 1140/2020 to 1120/2000. Other that slightly lower green line, nothing else changes. The blue line still varies alot. Stale shares still the same.

One thing I did notice on claymore is that the hash rate for the cards do varies quite a bit once in a while. It seems to be stable ~29.4mh.s, then it will be come 28 or even 20. The next time it reports the rate it back to normal. Claymore does not report real time unlike ethminer so its hard to know whats going on.

Sorry for my long thread, any help of tips would be greatly appreciated!!

Thanks!!