My view is that you will only encounter the limits of the 964 standard setup on a track (no personal experience) or on an Autobahn (personal experience).
I noticed occasional brake fade on the Autobahn in my 964 (and on all of the three previous Porsches that I have owned). But this is only after repeated heavy brake application at speeds considerably over 100mph unique to a congested Autobahn. Because brake fade arises from build-up of heat in the discs, and heat is a function of energy dissipated, high-speed braking puts much more stress on the braking system than low-speed braking, even if the same speed drop and same time is involved. That is, 130mph to 120mph in 10 seconds is much harder on the brakes than 90mph to 70mph in 10 seconds since 60% more energy needs to be shed in the same time. This is because energy increases with the square of the car's speed. I cannot imagine that you would get anywhere near the start of brake fade on UK motorways; if you did, the expiry of your driving licence would probably take place before the expiry of your brakes!
So, in the UK and most other places, for road use, I do not think that there is any performance benefit for road use. That is my personal view. Maybe some think they just look better, but not to my eye.
One little tweak that I made was to change the flexible hoses for steel braded ones. I had to do mine for the MOT, and the steel braded ones were about the same price as the ordinary ones. This made the brake pedal feel excellent. This was not just because my car had soggy brakes - I have driven a load of 964s when buying mine, and I know what the brakes are like - and the steel braded hoses do seem to make a difference.
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