i would go around with one of them without fixing her and check where are the hottest spot in the case so you will how the fan controller react and get the best spot
Hsf and Cpu muffin? One would do the job of both there
Save one for outside the case Op, its handy to know the ambient temperature as well
Cpu
Gpu/Gpu's
Nb
Outside
Is my opinion, use one on Sb if you only have one Gfx card
Moto