I am looking into the Schaeffer 7000 product line and there is a local dealer by me that sells it for a good price. The only thing is I want the 5w30 and he says he only carries 10w30 for the 7000 line. Is there really much difference, the car is an 05' Corolla w/90K miles which calls for 5w30 in all climates. The car is mostly in Phoenix, AZ but on the weekends goes up to Payson, AZ which gets in the 20's in the winter time. I really think I'm probably overthinking this but just want to be sure the 10w30 will be a good choice year round. BTW, Here are some stats on the oils. 5w30 10w30-Viscosity 40C_47-52, 62-72 100C_10-12 10-12 Thanks in Advance.