I gutted my pipes too and have a measurable gain on the dyno. That being said I do not have straight pipes, there is still back pressure but only a reducer cone no baffles. I have also done other mods though to go with the pipes. You need back pressure or you lose power and you will not gain by simply allowing the exhaust to flow better. You need to make intake and fuel changes to go along with the open pipes.

I learned all I need to know about life by killing smart people and eating their brains.
Eat right ,Exercise ,Stay fit, Die Anyway!