Even so as a captain of a 767 you should have an idea of ZFW, Fuel weight and payload and the rough relationship with take-off speeds? It is fundamental.
For a couple of years I was involved with a company which operated a 737-800 fixed-based simulator (usually used by cadets for pre-sim assessment practice). Now I have no real-world experience of flying jets but even I know that the ballpark take-off speed is in the 140-150kts range.
If I was in a real one I might be out by 4-5 kts if I did no prep but not 40!!!