Well just doing the math... stock 05 xterra at 265hp add KN cool air and Gibson cat back each worth up to 15 hp extra that's 295hp... what about a throttle body spacer or retuning timing with one of the various units for sale out there? Seems like getting another 5hp isn't out of the relm of possibility... I realize that your X only cranks out 190hp and 300 seems pretty far off from there but there must be some less than extreme modifications out there