Just chiming in here since I had experienced the same issues and wound up buying a street perf. 19 row oil cooler. The reason I went ahead and splurged on one is due to the fact that after I got my Z and would get on it just a little I would notice the temps climb dramatically from 190 to 220-230 fairly quickly.
I called up Nissan and they said it was a known issue and that I may want to look into getting a performance oil cooler for it. This kind of ticked me off being that I had just bought it and you would think they would have corrected this themselves since it can cause your engine to overheat and do a "shut off" on you..
So 'Nuff said I have had no issues since installing it.
'09 F.I. CBE/HFC-Stillen Gen3,Setrab +ModBod