T3 vs T3x actions are the same metal make up
T3 vs T3x, recoil lug is bigger, metal bolt shroud, different tapped wholes for a picatinny rail, better reinforced stock and recoil pad.
Barrel/action is the same profile size, but it just different metal material between the blued/SS.
you can prevent rust by taking care of the metal. I love to practice shooting in the weather (rain/snow) but I always make sure that I wipe it down with a gun oil rag before I store it back into the safe, if it got watered on.
If you find a screamin deal on a T3 I wouldnt hesitate buying that over a full priced T3x. I look on Asmslist all the time for T3 because I know im going to change things out on it and ill take a good deal any day.