I went the 2.75" and the chip at the same time, both made a hell of a difference, but i do know from others that the bigger exhaust does make a difference, some say it gets rid of a fair bit of the turbo lag that is common with the Navaras. I would recommend the Beaudesert as the bends are not creased , but i would go bigger than 2.5", either 2.75 or 3"
cheers,
Lance