In regards to exhausts, everyone will have a different opinion.
What you really need to look at is what your usage of the car is and what you will get out of each type of header/exhaust.
Personally I like a H-Pipe over a Kiss/X-Pipe, as the H-Pipe exhausts tend to cackle and burble a lot more on overrun like an old school V8.
If you want the highest number on a dyno then 4 into 1 headers with a 3" exhaust seem to be the go.
If you want more usable power on the street then Tri-Ys seem to be the preferred choice but will flatten out very high into the rev range.
Sound plays a big part for some and the extra power is just a bonus, in which case it doesn't matter what the setup is exactly as long as it's pleasing to the owners ears.
Some people use their car for drag racing, others for track days, and most for getting from A to B.
Each setup will suit a different purpose so you need to consider this when looking for a product that will suit YOUR needs, not someone else's preferred setup.
Now, on to diff gears. It has been said by many an old timer that the quickest way to go fast is to change your diff gearing.
No matter what setup you have this is the single most quickest way to improve your perceived acceleration.
You might lose the use of a couple of low gears but you'll take off like a rocket providing your tyres are up to it.