Disclaimer: We travel really heavily and we have never been charged excess baggage IIRC (with one exception - charged 100 CHF to check a fifth (!) piece from ZRH-YYZ on AC in J. Allowance was four bags.)
Trip <4 days: 1 bag usually around 22kg
Trip 5-9 days: 1 bag usually around 30kg (if flying J) or 2 bags around 18kg (if flying Y)
Trip 10-21 days: 2 bags usually around 20kg each (Y) or 2 bags of around 25kg (J)
Trip >22 days (summer travel is usually 2 months and usually / always in J) 3 bags of around 23kg each.
Yes we travel with way too much. Yes it is stressful. However, I always justify it by saying that I would rather have a little extra hassle when travelling than forget something really important. We have never had a problem fitting the luggage in our car
Cheers,