I use Fuchs Titan Supersyn 5w-40, it is the BMW recommended long life oil for this engine, the 30 will be thinner at higher temp than the 40, so I assume you would not see it being sluggish on this basis...... Will,it cause problems in hot climate, I don't know as an academic on oils but would assume it might being thinner and you may burn more oil past the rings. But then again it may not cause problems, one of those suck it and see things I guess
Best to stick to oem recommended oils for conditions and climate.