I use synthetic 0W30. Did the Amsoil rep recommend 5W20? Seems to me that the 5w20 would provide less protection over a narrower temperature range and provide worse fuel economy, but I may be way off on this. Probably someone here can accurately explain the meaning of the numbers.
Not to say that your way off but... the 1st number is the viscocity when in a cold engine. A lower number provides easier starting. The 2nd number is the viscocity at temperature. A higher number will be a little harder to pump so gas mileage will suffer. The Insight manual recommends 0w-20 because the engine was designed for minimum friction so a heavy weight oil is not needed to withstand the high temps.
Hmmm, around here the used oil goes into the tractors and eventually the chainsaws etc.. We would Insighters have to change our oil 12 times or more to use the equivalent of one fill up of a Jetta diesel. If changing the oil too frequently prevents the cost of an engine rebuild or a car replacement, I think it is cheap insurance. Honda must have some reason for the Canadian rating, eh? That said, synthetic oil is supposed to last twice as long as Dino oil, and if you install an Amsoil bypass filter system you should not have to change your oil at all (in theory). I suppose those who really want to save the planet should definately install a bypass system. I'm still sitting on the fence, ouch!