If you're planning on staying with the stock turbo, stay with a drop-in replacement model. Bigger units will have more pressure drop, and the stock turbo will struggle to keep the same amount of boost while filling that volume.
Mishimoto IC on my EB was by far the best bolt-on mod I've done to any boosted car I've owned. The stock IC really struggles in the humid summers down here. Based on my own seat of the pants feeling (as well as Weather Man's data above), the drop-in units have very few negatives down low only adding a slight lag due to increased volume, but large benefits up top in the rev's. Some of the larger units will have a bit more lag and lower power down low, while not providing much additional cooling over the smaller replacement units.
Ultimately, anything is better than stock, and you really can't go wrong. Throw the stock in the trash ASAP and get something else in there.
