What is the heatspreader temperature rise with the heatsink and fan attached?
It is typically 3.4°C/W. Keep in mind that the heatspreader is a part of the device, and the heatsink and fan are separate pieces, so with the heatsink or fan not attached your heat dissipation will be less. If in doubt, use the Safe Operating Area Calculators. There is also an Application Note (AN-LDTC01) that explains the Safe Operating Area in greater detail. These will help you determine if you need the heatsink and/or fan so your devices are not damaged by too much current or too high a voltage.