I'v done all the digging I care to do and it seems no one has done proper testing on the Elemental Resistances. There is a bit of information here and there but nothing complete. So, I'll be the one to do it!
There is a great deal more detail to be discussed but forum lengths get in the way. You can find my full write up HERE.
And if you want to access the raw data and most of the math i did you can get it from HERE.

For those of you who want to cut to the chase here it is:
These are some APPROXIMATIONS i have been able to make.
1) The range of damage decreases by about 0.120% per 1 resistance increase.
2)Number one translates to a decrease of 0.165% in the CRIT range per 1 resistance increase.

Again, sorry for the brevity. 1000 characters is nowhere near enough to present this well.