Hi David,
The reason for running 40:1 is for better lubrication,I run my 385XP at 32:1 with Maxima K2 synthetic oil..Most people think you will be fouling plugs left an right but that really is'nt the case as long as everything is adjusted correctly you will never have that problem..I would suggest you run your new saws at 40:1 especially during the break in period..Hope that helps
Rob.