Hi Andrew, and welcome to the club.
I am inclined to agree with Rodney. A turbo charged diesel has plenty of power, especially from 30 mph to 70 mph. Its there when you need it. The design engineers are pretty good when getting the power to weight ratio right.
Jaguar used the same engine in the XF and in the Estate version and it could easily pull a heavier car.
Years ago, in my motorcycle days, a mate had his 250 cc BSA speeded up, and he claimed it would do 100 mph, and it dis, -- for about 10 seconds.
The X type is a nice comfortable car and you will enjoy it as it is. It will save you a few shillings, too.
Regards,
Peter.