On a 535HP engine I've done dyno tests with H, X and no balance tubes with mufflers.

An X will show about 3 HP and 12 Ft Lbs of torque over nothing and an H shows about the same HP but only about 4-5 Ft Lbs.

Tone (noise level) definitely changes but I doubt that 2 people in the entire universe will agree on any one sound being the absolute best.

If you have room run the X, if not run the H..you probably won't feel the difference, although you may convince yourself that you do.

On a side note I also tested Dyne Max Super Turbo mufflers against Flowmasters and the Super Turbos made slightly more power, but on the track the car ran an identical 3 run average with both sets of mufflers..go figgur