Help Choosing Best Fire Damage Staff

[SkyrosX2]

Hi, everyone!
Which one is better:
1: +1 All Spells, 32% Spell Power, -15% Target Fire Resistance
2: 31% Spell Power, -20% Target Fire Resistance

So, the damage of Apocalypse is higher with 1 (1009-2530) than with 2 (961-2389), but at the same time 2 has the best -x% resist.
So, how do I know which one I should use?

I'm not sure this is an ok analysis (I have no clue if the -x% resist is applied like I considered below; is it???), but I did this to evaluate the average damage by each staff:

Staff 1:
1009*1.15 to 2530*1.15 = 1160 - 2909 (damage dealt after considering the -x% resist effect).
(1160+2909)/2=2035 (average damage)

Staff 2:
961*1.2 - 2389*1.2 = 1153 - 2866 (damage dealt after considering the -x% resist effect).
(1153+2866)/2=2010 (average damage)

If this is correct, Staff 1 would be slightly better.

What do you guys think?

Thanks!!!

[SkyrosX2]

Oh, I also have another staff like this:
+2 To All Spell, +21% Spell Power, -13% Fire Resistance

Doing the same analysis as before:

1111*1.13 to 2553*1.13 = 1255 - 2884 (damage dealt after considering the -x% resist effect).
(1255+2884)/2=2070 (average damage)

So this third staff, even though it has the lowest -x% resist, would actually be the best among the three.
What do you guys think?