i'm not sure what the legalities are in america, but in australia, there are big fines involved if you gut your cat.
a few years ago i read an article by a performance car magazine that made an attempt to stop people from gutting their cat converters. they took a 200kw @ the wheels skyline with a good high flowing cat converter and they dyno tested it with the cat and then without, the car only dyno'd 2kw extra with the straight pipe. the car mag also mentioned in their article that the 2kw could be due to temperature changes or anything else minor that changed between the dyno runs. problem is though, i think every git that read the article thought that they could get 2kw from their hyundai getz if they put in a straight pipe.
if i were you, i'd go buy one of these:
http://www.verociousmotorsports.com/Shop-by-Category/Catalytic-Converters_2/Metal-Core-High-Flow-Catalytic-Converterit'll keep you out of trouble with the police and the epa and you'll also get your extra 1kw over the stock cat
also, i will add that i ran a gutted cat for a little while, the cat needed replacing and i didnt have the money to do it, so i gutted it to keep running my car (it was bogging down etc) the exhaust noise was absolutely ridiculous and the stink was horrendous.. but it did seem to go faster.. probably because of all the noise more than actually going any faster.
it took a total of about 2 months before i was sent a letter from the EPA for noise & to check if the catalytic converter was installed.