I've been experimenting with Radiation Resistance and noticed an odd behavior. I did some testing at the radioactive brown pond north of Big John's Salvage (which is pretty radioactive but not enough to kill you too quickly) and these are the results:
When I enter the pond without any protective gear (0 Radiation Resistance) I get around 50 rads.
While using Power Armor (1050 Rad Res) the same places gives me around 15 rads.
BUT while wearing the Hazmat Suit (1000 Raz Res, 50 LESS than the Power Armor) I get only 2 (yeah, TWO) rads.
It seems that the actual Rad Res amount is irrelevant, the game takes into account what gear you are wearing at the moment and make an internal calculation of how many rads you should be taking.
Either that or my Power Armor has some leaks...