Fan speed cannot change the hashrate power.
this. and if your running it 40 degrees+ then youre not doing it right. read the specs. the safe max temp is 40
i adjust fan speed all the time depending on the temp since i live in south florida but I never come off 10ghs + or - a little.
as i understand, baikal states "operational temp 0 - 40 C" is ambient tenperature. Not chips itself.