you could consider using ur 4 inch inline and use it to help extract allong with ur other fan !!! one fan pushing and the other pulling !!! now i dont no even if its doable but i had similar probs not as high as 35/40 thats sahara desrt shit man, but i am considering it for my next grow as these summers r killers,,,,,, plus there will allways b ample air in the closet coz ur in and out of it often enough to give it a good suply of air, worth a try if theres no better sugestions !!!! good look in wat u do man