Regarding engine upgrades, the best way to start is having a sound platform to improve. Have a compression, or better, leakdown test done to determine present sealing condition. Then move on to your ignition system, fuel system, including injector's spray pattern and flow, then check fuel pump pressure. Your transmission (if auto) might benefit from additional cooling, check the condition of your axles and CV joints.

I don't have much Volvo experience (yet!) but these are guidelines for any drivetrain performance upgrade. I've experienced "hot-rodded" bikes and cars that didn't run as well as a well maintained stocker because aftermarket parts won't make up for a problem elsewhere.

For brakes I'd go with the stainless lines and good pads.

Not to say I don't want a sport exhaust, sway bars or cool-looking cross-drilled rotors on my '95 855t but I'll make sure everything else is in order before spending money on upgrades.

Just my humble opinion,
Erwin in Memphis