You can tell equal length headers will help, may not be able to feel it (Seat of the pants thing), but they should help over the stock units. The 2.5's will do well with those style of headers over factory ones anyway, you get the collection with a little more pipe travel, thus raising the peak of the band which 2.5's like to rev anywhoo.
Headers are something I'll do, but leave the cats and muffler alone. Don't like loud cars.
