When I put a Megan CBE on my LGT's Cobb DP I did so as part of preparations for a turbo upgrade. My LGT was on meth and tuned to the limit so while I didn't expect the Megan to provide a lot of power, I expected something. Never saw an ounce of gain despite countless logs.
Kind of frustrating, and counter intuitive.
My STi came with the SPT exhaust, and I think it is the perfect exhaust for my car. The SPT on my 11 WRX started to become annoying after a couple months and I'd have gladly traded it for OEM. But it was a hatch as opposed to my 4dr STi, and the exhausts are completely different except for the name. On the STi there is no drone, and the exhaust, while perhaps again being no power adder at my whp, is the perfect exhaust for this car IMO. It is in context.
A CBE's value, therefore, is relative, and not referenced to horsepower alone. In fact, I'd say the vast majority of people who install a CBE do so for other reasons than horsepower, while hoping it's worth a little. Guilty.
For sure it isn't holding me back... the catted DP takes care of that, but I'm good with that, too.