Most aftermarket (tower) coolers blow air to cool the CPU only. The stock cooler blows downward towards the motherboard, so cooling all other motherboard components, the VRMs/MOSFETs inclusive. Low end motherboards usually do not take overclocking into account. Max TDP is rated based on operation at stock speed on the stock cooler; nothing more. To be running a cooler other than stock would be pulling away from this certification, in addition to totally removing all cooling (airflow) from the VRMs. Where there is no airflow, heatsinks can, however, help with the heat dissipation from the particularly fragile MOSFET chips - at extra cost.