SCR, I know that you have the Gibson SS, but how much difference in performance between the two we are talking about?, although I like the dual look, I am not going racing or Hauling more than 7500lb.
Gibson makes three cat back systems- The Dual Sport, where the two pipes exit side by side where the stock exhaust does; the Swept Single with one 3" pipe exiting at the same location as the stock, and the Extreme Duals, where one pipe exits in the normal place and the other crosses over to the driver's side. The Single produces 5 to 10 more horsepower than the others do, with the gain in the 1,800 to 3,000 RPM range, where we drive most of the time. The other two make their HP gains at a much higher RPM, where it isn't much use to most drivers. All three systems are the same back to the muffler. The difference in the mufflers is the single has one outlet and the duals two. Of course the tail pipes are different on all three models.
I don't like the Extreme Dual setup because the left pipe crosses over between the diff and the spare tire. This can cause heating of both the diff and spare. This pipe also comes close to the air compressor for the rear auto leveling, causing heating. These problems, plus reduced performance gains ruled out the Extreme Duals for me. I like the looks of the Dual Sport, but it also makes less power than the Single, and, like the Extreme Duals, there are two tail pipes going thru the same space over the rear supension. They take up more space, so end up being closer to items which could lead to heat damage.
Since my purpose in changing the exhaust system was for power increase and fuel savings (and still sound good) the Single was the clear choice.
The Single produces a 15-20 HP gain; the other two produce 10-15 HP gain. But as I said in earlier posts, to gain the maximum from both a exhaust system and a CAI you need both installed.
I hope this can help you decide which system to get. I think the Single is the best, for all the reasons I listed above, but you will have to decide what is best for you.