When I get all 4 wheels up in the air at the same time, I use 6 jackstands and one jack. I don't trust just 4 jackstands. Typically one of the 6 is not touching due to the lift points/weight distribution, but it's there 'just in case'. I typically move the jack around too, if it's not in my way of working.

I'm by myself 95% of the time I'm working on the car - so I'll take the time to use the extra stands.