Everyone swears highflow cats flow just as free/good as having No Cats.
Everyone calls no cats crazy loud it all depends on the muffler setup you are running.
And just as powerfreak said there is really nothing to gain in taking your mufflers off at the track if you are going for that add some exhaust cutouts. QTP has some nice electric ones where you can open them up and close them ready for street use.
Ted from Jannetty racing did a test on no cats vs. high flow cats and the results were that running high flow cats won't cost you any extra horsepower. Running no cats also gets a little stinky at stoplights. High flows also deepen the exhaust tone a little compared to no cats.