As far as I know, the stock Fan and shroud is the best cooling option. It just creates a bit of load on the engine and takes a little power away, which for normal use, is not an issue.
If you are trying to get every little bit of power out of your engine, then taking away that load might make a small difference. Might aswell get an electric water pump while your at it for the same reason.
I got a Brand new Aluminium Radiator off Ebay for $149 posted. (Autotechnica M-spec) and it works a treat and appears to be good quality.
The guys who installed it for me + new thermo and hoses, reckoned it was the best money I will ever spend on my car.
Shop around.
A radiator cooling panel may help also (and they pretty things a little. Bonus!) but NISSANs design should work in stock form unless there is a problem.