For Honda, just go with whatever Honda recommends.
And in case you question why not thicker, there's an SAE report (dated around 1998 or 99, submitted by HOnda engineering research division) that they are going after thinner oil with well-justified results and such for thinner grade.
Lastly, there's already a guy on the board who lives in Mojave desert running M-1 5W20 on his wifey's CRV and the results is nothing short of impressive.
Q.