I didn't like the idea of making a weird Cafe racer from the rocket... and totally agree, while that exhaust makes sense for symmetrical people, you are losing a lot with that... I will be fun to see somebody riding it when the rain starts...
This is a very controversial subject, suffice it to say that all engines are not created equal.
The highest horsepower (cars top fuel dragsters) run open headers but that doesn't mean that all car will make more power without ANY exhaust pressure. There are MANY factors involved in the intake and exhaust process!