With the fantastic ballistics of today's premium sabots you will likely be setting your scope up to shoot bullseye at 150yds. This makes 200 yd shots possible with only 6" of hold over. Not only do you need a good rest and practice to shoot these distances but you also need optics that allow you good shot placement as well. If you plan to shoot less than 100 yds magnification is less important but if you want to take advantage of the full potential of a good rifled barrel i suggest at least a 2-7x or a 3-9x specialized slug scope or a decent rifle scope. The bdc style reticles on the specialized slug scopes are a bonus and I believe most of the quality manufacturers produce one. Leupold, Burris, Nikon, and Bushnell all come to mind. Regardless of the distance that you want to be prepared to shoot confidently at, do not waste any money on a poor quality scope as the recoil will destroy it quickly.
Brad