I would stick to stock brake components. After-market pads may

have problems with squeeling (frequently reported) and may not

provide as short stopping distance (sometimes reported here).

Are you specifically trying to address something about the stock

brakes you don't like? If they work well enough for you then I'd

stick with stock parts.

Undersize means the rotor thickness has worn down (pads and

rotors both wear). Feel around near the outer edge of the

rotor and you will feel a lip. When new, the rotors were

flat and there was no lip -- that is the amount of wear.

(The amount of wear is surprising and you have to double what

you feel since the other side is worn, too).

Rotors typically last for 2 pad changes. Volvo rotors should

not be turned -- just replace them.