amsoil

I have a 04 FE450 Thinking about changing to Amsoil Manual calls for 10/50 Amsoil makes 10/40 or 20/50 Which one can I use or should I stick with 10/50 Thanks Frank

I am thinking of running either amsoil 20w50 or motul 5300 semisynthetic. what's better! I will be riding on the streets 100% (20%) hard. should I change my oil every 8-10 hrs or by running amsoil are the oil change intervals pushed back. I know on a car with amsoil you can go more than...