Headers?

longtube headers makes more torque at a lower rpm.
longtubeheaders makes it alot easier to build any type of exhaust.
bigger exhaust AFTER the headers wont cost any power at all. fourstroke engines dont need backpreasure in fact they suffer when backpreasure is added unless totaly backwards built.
bigger exhaust usualy gives you a bigger sound,not nesesary louder but bigger,deeper. depending on mufflers and enginespec,this is up to 2½"tubing,3" usualy means that it gets louder and harder to get quiet.
dual 2½" exhaust is plenty up to about 450hp up to that point 3" bassicly only adds noise.