idk wit the temp issue but to give yourself some options check this outHow much more heat does a 600 watt put out compared to a 400
2 600 would just be heat overload unless you were running 2 cool tubes 600 watt and a couple extra fans
yo wiseguy, i have a 400 in veg and two 600s in flower roomjust a guess here , but I think it's going to put out 200 more watts worth of heat...lol. sorry couldn't resist