10w40 is what Vauxhall recommended for my 2000 Vectra B z22se, for annual mileage of 10k 2 oil changes a year.
5w30 is more for high drain intervals, 20k+ per year where the car is used for long journeys.
I found mine burnt more oil and rattled more on start up with 5w30. that was at low mileage, 30k ish so went back to 10w40. didn't have any rattles and chains where still sound at 117k when head came off for porting. crank was still spot on, only problem was with No 4 bore which was close to max ovallity at 1 point of the bore.