Miller, general rule, the least amount of back pressure after the turbo the better, but you also have to keep in mind the exhaust velocity exiting the turbo, usually a larger downpipe is better, but there are negative side effects of goin too large
run a proper size exhaust for maximum flow with a straight through muffler and run the cutout some where after the downpipe before the muffler, that is where i think it would do the best benifit, though im sure there are others on here with more experience with the cutouts