where do you cross over your ht setup

hello. i am just wondering where everybody else crosses over there ht system at. thx says 80hz with speakers set to small. some speaker co. say set front mains at 60hz the rest set at 80hz set to small. i even read one speaker co. in a reveiw say 20-30hz and set speakers to large. if you are driving a full range speaker system with a stand alone powered sub what do you fellow audiogoners find best. also when using a spl meter do you set up your system at 75? thanks.