Hi was wondering if anyone knew how much performance is actually lost going from 5w30 to 0w40 if any at all?

Reason is because I always use Castrol Edge 5w30, never burns any oil though. I'm reaching 5,000 KMs soon and its been about a year so it definitely needs a change. I want to change from Castrol Edge 5w30 to a proper synthetic.

I heard that Mobil1 5w30 is a Group III blend oil? and that their 0w40 is a group IV oil? Can someone confirm please?