Volvo make the best car they can to conform to the confines of Euro regs. They then go even further with emissions reductions to get their cars into lower tax bands (to increase sales). If you remove these considerations (as you do with an aftermarket remap) you can make a more efficient better performing car.
That said, I'm with XC90mk1 - I wouldn't bother.
You say your D5 is now running perfectly. If it 'aint broke, and all that...
