I'm not really into exhausts so to speak, but I did want to drop some weight with minimal hassle. So, with the Borla cat-back system for 'inspiration', I had a local shop fab up a system.
First, they removed everything starting from just forward of the small box resonator. Total weight removed according to my scale was 42.7 lb (3.8 box res + 12.5 mid/resonator assy + 26.4 axle back assy). They replaced that with 16 ga 2.5" OD SS tubing, a centrally-located Borla 40942 muffler, and more 16 ga 2.5" OD SS tubing. That's it - single exit, no tip, just functional. Total weight added back was ~20.6 lb (8.0 muffler, 11.6 pipe, ~1 for unmeasured hangers and welding), so the total savings is approximately the same as a muffler delete.
I don't put a lot of stock in exhaust videos, but I put this together just to see how it would turn out and compare to other videos:
https://vimeo.com/61769432
I tried some inside shots with the gopro mounted to the side window, but at moderate revs you can't really hear the exhaust at all over the wind, road, and mounting/housing noises. In person, there are a couple interesting resonances in the 2k-3k range, but nothing bothersome and overall I'm satisfied with it.
As far as any power increase, I have no idea. I have no plans to dyno it and the axle-back part is 'crush bent', which probably compromised the benefit of the 2.5" a bit.
cheers!