On the brake rotors, unless you plan on going to the track and need the extra diameter to manage heat, I would keep the same size.
Because larger rotor is extra rotational mass to move.
Get a quality 2 piece rotor with aluminium hat so it won’t rust like you have now, and it will be lighter than those stock rotors.
It will be acceleration friendly.
And still give excellent stopping.
The rear callipers on Mustangs, despite being small, are quality and perform very well.
Rotors like a Baer eradispeed 2 piece with aluminium hats.
Or Wilwood equivalent.
Smooth face or slotted only.
Not cross drilled.
Cross drilled can crack, and collect brake dust in the holes.
No noticeable or measurable gains, and the brake dust rusts when water touches it.