10w or 60

had some oil delivered...8 bottles....ordered 10w/50 but 2 out of the 8 was 10w/60 foned dealer,,said that 10w/50 is being replaced by 10w/60 and ktm/berg run better on 10w/60 he even said he spoke to motorex rep & assured this is the case....ummmm not so sure,,,what u rekon???