I have run 245/50-16 o my 2000, and some have gone up to 255/50-16.
I would recommend these.
http://www.tirerack.com/tires/...1=yes
I have them on a lighter car, and they are pretty good. Not PS2, but better than most other non-Tier 1 maximum performance tires.
Or the Goodyear F1 if you have more money to spend.
Tires are important in that they are normally the only part of the car touching the road.
Read the tire sticky in Infiniti General.