Online Autosport told me that years ago when they did a 1.8 to 2L conversion, it made better power than the 2L 8v engine did with similar mods. The reason was that the 18SE engines have a better throttle body - an oval jobby. They also reckoned that the 1.8 has the best cam profile.
Finally, the 16v has uprated con rods over the 8v. Useful info.