I use 5W40 in my M51 engine and change at 6K miles. Brand is not important, I use Total or Shell Helix whichever is on promo at the time.
It tells you clearly in your handbook which oils are recomended for summer/winter temperature ranges. Personally I would not use 5W30 in the UK in summer.Would it be safe enough to use fully synthetic 5w30 instead of the 40 chaps?