Interesting to know, i don't think i waited 60 seconds to find out if it would auto kick in.
also, are you running cgminer in linux? if so, which one would you recommend or doesn't it really matter?
also, is the sierra being damaged in anyway by setting the clock rate to 590? as i thought i read somewhere 612 was a sweet spot, i didn't fancy pushing it that far.
sweet spot differs from chip to chip. i'm not a chip engineer but i presume you could damage any chip if you pumped too much power through it. but i believe ck said he'd spent a lot of time on the cgminer code for HashFast. so i'd say it'd be some sort of fail safe function. ck would have to comment, i haven't read his code. iirc he mentioned 850 was the limit
what i do know from practical experience is that if you hash with too high of a clock rate, the ASIC chip tends to stop hashing and cgminer will automatically lower the MHz after 60sec of no share received from the device.
Cheers,
QG