I have an '07 xc70 (it is the second generation xc70 with a 5 cyl engine, not the new 6 cyl) which I put IPD bars on. I don't feel much of a difference at low speed around town but at higher speeds, on a twisty road, the car seems much more stable. I was told that the XC comes with progressive springs so at low speed when the forces are smaller the ride is stiff and at higher speed when the forces of the turn build the springs get softer? I don't know if this is true or not but for me with the IPD sway bars, the speed at which the pucker factor kicks in is greater, than without.
P.S. the rear IPD bar is much much bigger than the factory rear bar.