Playing with my bike computer outside the supermarket, as you do, I noticed I now have a new max speed. The previous one was set about a month ago following a bus down a steep but short hill. I haven't been down (or up) any comparable hill since, so I think this one must have happened with a tailwind - it's been pretty windy here the last couple of days. Strange how I only noticed the extra effort needed for the slower speed into the headwinds...