This is what I go by as well, both for my personal vehicles and for the fleet we maintain at work. Never seen anything wrong with old oil as long as it hasn't obviously got water accumulated in it, which I've only seen a couple times on vehicles that have sat untouched for years. The last one was 5+ years outside in a damp spot.

 

Sticking to 5K then. Also a good reason to try and get the Disco out more often.