You can look for test results in "Denny a. jones,  Principles and prevention of corrosion". 

To quote from chapter 5 in the book Stainless Steels, pub. Les Editions de Physique Les Ulis, written by B. Baroux, G. Beranger, and C. Lematire, and entitled,  'Passivity and Passivity Breakdown in Stainless Steels',...

"In the austenitic steels, nickel does not seem to take part directly in the composition of the passive film, but acts rather as a moderator during uniform corrosion by anodic dissloution in the active region."

Now when you turn to chapter 18 in the same book, entitled 'The Duplex Stainless Steels', by A. Desestret and J. Charles, you find the following comments:- 'While nickel has a beneficial influence on crevice corrosion resistance, its concentration depends upon the overall balance between gamma stabilising elements, since experience has shown that not only corrosion behavioiur, but also mechanical  properties and workability, are optimized for a ferrite volume fraction of about 50 %. The best results appear to be obtained with nickel contents of the order of 5 to 8% [47-49]. Larger amounts increase the risk of sigma formation.'

In chapter 18 there are sub-sections on intergranular corrosion and pitting/crevice corrosion, and there are further references in them on the effect of composition (including nickel) on these modes of corrosion.

So my advice is to read those sections, and look at a few papers on this topic so you get a few opinions on the subject.

This is a start for you.

Thanks