Humidity plays a factor ,i find my plants can tolerate much higher temps with very low humidity
My flood tables are light via 3 600 HPS per table with 34'' X 38'' air cooled hoods ,the hoods are cooled using dual high cfm 6'' fans in a push pull configuration , even with the massive air flow going thru my hoods my rooms can hit as high as 88 degrees durring june & july , the reason is from radient heat from the light/lumens so im familiar with your exact situation.
Running a 600 watt at 75% is roughly 400 watts which has very weak penetration ability as well as a light spread thats too small to effectively cover your 3 x 3 area ,you need to turn the ballast up to the full 600 watts.As long as you can keep temps below 90 degrees & humidity at or below 50% your plants will suffer no bad effects from the increased heat & lumens.
Plants are much like humans , the lower the humidity the longer we remain comfortable in hot enviroments , mj plants are much the same , as long as they are comfortable with the enviroment they will flourish .