It's amazing how much more heat those pads need. I usually run the iron 340-370°C. Use the side of the iron, rather than the very tip, put a little more pressure on both the pad and the wire, and take a little more time. Still, it's rare for solder to flow through to the other side of the board, which I usually see on most non-thermal pads. Oddly, when soldering power jacks into 4.8mm holes, I seem to have more than enough heat.