MB Oil Recommendations

[bobbo]

I worked in the automotive parts business for about 25 years and sold a lot of oil. Many customers used Castrol 20w50 and so did I for awhile. A few years back I researched the SAE web site and saw that they reccomend no more than 20 points difference between the numbers on either side of the "W" in the oil's weight. I recently had our '99 E320 serviced by a MB certified mechanic who told my wife we had used the wrong oil (10w30). They put 5w40 in it. I thought an oil like that would be more suited for northern climates where there is extreme cold. In south Georgia do we really need an oil like the 5w40??

Thanks,
Bobby