3,000 miles or less for me. I stick a floor jack under the passenger side to get that extra little bit out from draining out of the drain plug.
For a while my wife was commuting 125 miles/day (non-MBZ). To keep from going crazy with oil changes, I would go 10,000 miles on Mobil 1. At the 5,000 mile mark I would spin a new filter on and add 1/2 a quart. Worked like a charm. I trusted the oil, but I worried about a clogged filter.
I've never had the problem with gas diluting my oil.
Experience is something you don't get until just after you need it.