As Ramrod says, stainless braided covered brake hoses make a noticeable difference even on just front brakes. Quality pads and discs, flushing the fluid and using quality fluid is a start.
Changing the cylinder bore with no knowledge of brake systems design is not ideal particularly when ABS sensors and controller are involved plus not a inexpensive solution…
Larger diameter front discs from turbo models is good upgrade and caliper brackets come with them.
Whilst all above makes for a better experience, a change to aftermarket fronts would be easy and more cost effective than playing with master cylinder options.
Talk to DVS Performance, he knows Volvo and knows performance brakes and suspension, he can advise and supply all of the above.
