Hi Shaun, the variance likely comes about because there is no drain plug on the 5.0 S/C engine and the oil should be removed by "vacuuming" out via the tube designed specifically for the task. You are then required to replace the exact amount removed and thereby avoid over filling. That said, the following should be adhered to, including the oil removed with the filter replacement:
Quantity: 7.25 Litres
Type: 0W-20 or 5W-20
Specification: Fully Synthetic to Jaguar recommended spec. WSS-M2C925A/STJLR.51.5122
Hope this helps.
N6 JMX