+1 on the weather.
One of our thoughts was NOT to spend the last days in the highlands, so there would be time for troubleshooting if we had run into trouble. Weather can change quickly, and you don't want to be trapped on the wrong side of the island. It might be impossible to ride hundreds of kilometers when the wind is literally blowing you off the road.
Hence I'd save either the Western Fjords or the Golden Circle for last.
If you're into photography, you may also want to consider the sun position during the day. The gullfloss for example is much less impressive in late afternoon, when the sun is hidden behind the hills. (Ask me how I know ...)
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