Torsion Bars...eh?

I am wondering if i should get new torsion bars for my ride. I am swapping out a /6 with a 318 and wondering what diameter of torsion bars i need, or if i need any at all. I have heard that a few guys prefer /6 torsion bars with their v8's. Can anyone give me a reason for this? And what would be the best route to take?--/6 bars or new ones?
Thanks,
Joe