We did test a Borla, it was the 14" case size, offset-center configuration, 2.5" in and out. Also, the Magnaflow mufflers are in the chart, only in disguise. If you look at the ones marked Straightline Performance, you can substitute Magnaflow, look at the sizes, and then see how they did. Not too bad at all actually, very well for the most part!
We saw a reduction in back pressure at the engine and a sound level reduction in around 75% of the cases we tested when using an X-crossover as compared to an H. We used a Dr. Gas unit; homemade ones will not act the same so it is unfair to group all X's together as it would be to group all H's.
Tom