The "Nismo" European radiator that was made for the Z is a good choice if you want no hassle installation and a cooling upgrade. It has more cooling fins than the U.S. spec one. It is the radiator I went with many years ago when I replaced my original one and have had no problems on spirited long high speed drives with the Z club guys or in a few track situations.
Regarding the electric fan clutch, most will say that staying with the stock set-up is better than an electric set up as there have been posts on here about problems caused for those using an electric set up, and that any cooling or performance gains are negligble from the electric set up.
