I've been tinkering with brakes on my S60 a lot, as has been documented on this site, I've installed everything from S60r calipers to both 328mm 2-piston front rotors/calipers from the XC90 to 336mm rotors and huge single-piston calipers. All worked very well with the 336mm being probably the most bang for the buck with relatively few mods.

I only ran into reduced braking when I ran heavy 18" wheels. I drive in western mass a lot which is brutal on brakes with his twisty roads and elevation changes.

So, I had a spare set of Porsche Cayenne calipers I pulled from my an Audi A4 I upraded. The radial mounts were close but def not a bolt on affair: i had to make a custom bracket from 3/8" steel and modify the rotor center bore to make it work. I'm running a set of 345mm Benz rotors and 15mm spacers so the calipers barely clear.

Anyway, thus far it has been an improvement over the already very good XC90 brakes. Its barely noticeable in regular street driving but has beem a huge improvement over windy mountain roads.

 

cool. you should market your custom bracket!!