Kroil
http://www.kanolabs.com/
As to which penetrating oil is best, it is my running joke here that everyone wants a different one.
Guy A comes in with a can of green stuff in his hand and it is
"THE ONLY one that works,,,, get rid of that other stuff"
Guy B comes in the next day with blue stuff in his hand and you guessed it,,,
"this is the ONLY one that works,,,,,, Get rid of all that other stuff"
We keep about 6 different brands around so that people can rotate as they find what they like, and run into various situations.
At my house, Kroil, PB blaster, Yeild and MMM are on the shelf, and as someone else said, the Plasma makes them all look pathetic.
Different grades rusting.
I think you would find that the different rusting would result more from the quality of the bolts in question and what particular surface treatment they had and how they were handled as opposed to the particular base steel composition of the bolts.