Start with using something like Motul RBF600 or Castrol SRF.

Jaguar recommends Castrol SRF for CCB-equipped vehicles.

I don't regard the workshop manual as my Bible. Besides, don't you have the curiosity to find out the truth by yourself, instead of simply follow what other people are saying?

I am using Motion RBF600 for my track day. It certainly feels better compare to the OEM fluid, but the differences are not that big on the pedal feeling. That's why when my friend suggested heavy duty SS brake line, I'm looking into it.

I will ignore your unsubtle and unnecessary insult and simply point out that braided steel hoses have been used for some time on Jaguars. Because I would not want you to simply follow what other people are saying, let me share what is in the Technical Training manual for an earlier model, the XK150, regarding the braking system. This manual (Jaguar manual NP07, dated 02/2006) was produced as the training manual for Jaguar technicians at the introduction of the 07 model year XK. It might even be referred to as the bible. In the section labelled "Chassis Systems", page 27, in the section titled "Hydraulic Brake Actuation", the final sentence reads: "Braided steel hoses are used to connect the brake pipes to the front and rear calipers." This refers to the systems on both the XK and the XKR, the only difference between them being the size of the front brake discs - 326 mm on the XK and 355 mm on the XKR. Rear discs were the same on both at 326 mm.
Now, to be clear, this description refers to a braking system which is a much less aggressive system than the one we are discussing in this thread; it was designed for what is arguably a touring car rather than a full-on sports car - the F-Type. The basic braking system in the F-Type has front discs of 354 mm with optional systems that go to 398 mm - and while we are not speaking in this thread about disc diameters, these comparative figures are suggestive of the specification level of the braking systems in the F-Type. If Jaguar used braided steel hoses in the X150, would it be reasonable to assume that the system on the F-Type (X152) would of lower specification? I do not have access at the moment to the training manual for the F-Type, but both critical thinking and common sense suggest an answer.