Platinum would be good enough I would feel comfortable going all the way until the Maintenance Minder says the oil is done, which is probably in the 8000 mile range.
Any good syn would be.
In your relatively temperate climate, a dino 5w-20 would probably be ok, too... though I'd probably get itchy at 5000 miles.
Haven't owned an L-series, but a D17, F23 and K24 and they've all been very easy on oil.