Traditional or "pusher" brass breech for Sharpfire?

So I'm planning to brass breech my Sharpfires, and I was wondering how I could get the most performance out of the short barrel section, because I don't want my brass to extend past the barrel extension of the blaster. The normal way is to add 17/32 brass into the original dart chamber, then add about 5" of 9/16, as the main barrel. I know that 9/16 isn't very good for barrels, so I had another idea. What if instead of the 17/32 brass, I had some 1/2 that would act as a "pusher" with the darts actually being loaded into a 17/32 barrel. Which would provide better performance, a short section of 17/32, followed by ~5 inches of 9/16, or only ~5 inches of 17/32, with more dead space? All advice is appreciated!