Not really with the 320mm conversion.
You can, however, easily enough do S60R rears, but you then have a sliding caliper upfront and a four piston brembo in the rear, which makes no sense.
The cars are heavily front biased anyway, so there's no massive need for most applications to go larger on the rear, but aesthetically, with an 18" wheel, you're right, the brakes look small.
eg.
Painting rotor hats black and having clean calipers seems to improve things a bit, but by modern standards the brake package is quite small.