Magnaflow has always had a good product. I was reading a comparison between them, flowmaster and Borla last week. The car was a 70 Hemi Charger. They started with a basic dual system with factory replacement muffs then changed just the muffs and ran the dyno. There was a marked improvement with Magnaflows and a minor increase with the Borla bits but the Flowmaster set only increased about 1% over baseline although, they noted the tone of the flowmasters was better than the rest.
Then they moved to a flow bench with one half of the system (it was duals but both sides the same) First they removed the muffs completely to get a zero base. From there they tested each of the four mufflers. This time the Flowmasters did better than the Borla's but the Magnaflows did the best (next to no mufflers of course)
The results are confusing to me, I would think the better it flows the more HP you should get out of the motor but these results don't exactly match.
Our Nitro's are not exactly the same as the test vehicle in that it did not have any computer controls on it where we do and it had a true dual exhaust with headers but I still found it interesting. They did list the model mufflers that they used as well but my memory is not what it used to be, nor would they work on our systems since they were 3" in and out.
I don't remember who sponsored the tests, ( I have an idea but....) I have just spent the last 20 mins looking for the article again but have not found the link. I will post it if I can find it.