If you're looking for performance, its a good idea to use mendrel bend piping. Crush bends should be avoided.
From sentra.net:
"A proper exhaust system should be fabricated from pre-made mandrel bends, not crush bent muffler shop pipe. A good fabricator cuts these bends apart and welds them together to make an exhaust with no neck downs. Normal muffler shop pipe benders crush the pipe by as much as 50% when making bends. These stainless steel mandrel bends are made by Magnaflow. Once welded, these can be polished like chrome. A naturally aspirated GA16 should not use piping bigger than 2" in diameter. "
"If your engine is naturally aspirated, limit your pipe diameter to no more than 2" or you will lose some bottom end with no applicable gain on top. For turbo applications, 2.5-3" is the way to go. Try to avoid the typical muffler shop crush bends. You can buy mandrel bends from Kinsler, Burns stainless, or Bassani. That way your local muffler shop can cut and section these for smooth, non-crush bends in your system."
Hope this helps.