[Kracka]

Your car has serious issues if its taking until 5k rpm to fully spool. You should be hitting full boost no later than 3500 rpm's. Free up that exhaust and check for boost leaks then make your decision. Both are great turbos, but the 16G is more efficient and will spool slightly quicker assuming your 18G is also clipped (15* seems to be the norm for those). I had a ported/clipped Big 16G and loved it, I regreted ever getting rid of it. Is your 18G ported/clipped as far as you know?