Air Canada has a similar system to BA. Before take-off data is sent via ACARS to the performance computer. Take-off performance data is sent back to the aircraft in the form of a WAT chart (Weight Limitations Chart). This only applies to ACARS equipped aircraft.
Flaps 20 is normally selected for rough or contaminated runways as it ruduces tire wear.
Normal flap selection priority for the 767:
-200
1. Flaps 5 Reduced Thrust Packs ON
2. Flaps 5 Full Thrust Packs ON
3. Flaps 5 Full Thrust Packs OFF
4. Flaps 1 Full Thrust Packs OFF
5. Flaps 20 Full Thrust Packs ON
-300
1. Flaps 5 Reduced Thrust Packs ON
2. Flaps 5 Full Thrust Packs ON
3. Flaps 5 Full Thrust Packs OFF
4. Flaps 20 Full Thrust Packs ON
5. Flaps 20 Full Thrust Packs OFF
Best Regards,