I didnt read the ENTIRE article but I think one little thing needs to be noted to this..
You dont LOSE torque when you step up to dual 2.25" or 2.5" pipes.
Because the engine breathes easier, the torque is moved higher up in the RPM range. This can seem like you lost your bottom end power, and most people confuse it with this.
In reality, you still have that torque, it just peaks at a higher RPM than it did before.
2.25" pipes are usually best for anyone. You can step up to 2.5" pipes if you have some torque-y mods (ie underdrive pulley, gears, etc. ), this way these other mods will make p for what you "lost"