Couple Questions

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2 quick questions... first on the exhaust im goin to get the bassani cat back.. already got the x-pipe.. ive seen on there site the racing and sport competition systems.. whats the biggest differances other than sound maybe and if so on the sound how much diff is there.... also on changin your rear end im goin with the 4.10 gears.. what all should i make sure to get changed.. just the ring and pinion or si there more that should be done while im at it.. just tryin to get stuff so can save a lil money and have everything done at once.. thanks