If you have parasitic heat draw from surrounding bits, or the device itself I can not stress enough pre-heating the board/site. I'm just talking about a hundred degrees over ambient, not even close to soldering temperatures. It decreases the peak thermal load on the iron by... more than a little, when the iron is removed if your in a cold room it will help prevent thermal shock from rapid cooling.
Study IR soldering profiles sometime, there's a forced air pre-heat followed by a peak in the pre-heat followed by the application of the actual IR heat source pulse for a period of time, then the IR source is removed and the pre-heat source is lowered to allow anealing of the joints followed by ambient air until the joints have cooled to room temperature. These profiles aren't used just because they're amusing and complicated, they result in nearly perfect solder joints.
Study IR soldering profiles sometime, there's a forced air pre-heat followed by a peak in the pre-heat followed by the application of the actual IR heat source pulse for a period of time, then the IR source is removed and the pre-heat source is lowered to allow anealing of the joints followed by ambient air until the joints have cooled to room temperature. These profiles aren't used just because they're amusing and complicated, they result in nearly perfect solder joints.