Again, this will depend on so many factors. However, I think you will notice the car boosting up quicker (most dependant on whether the cat is still in place and if you have a bigger turbo elbow/dumppipe) and a few more horses and ftlbs over the entire rev range with most probably further up the range. If you don't have a bigger diameter dumppipe, I would tend to spend the money buying one first ! The difference will be more noticable.
But, that's just my couple of pence !