I feel it should be pretty easy to calculate but I always get confused.

For example, this item here:

http://i.imgur.com/8tMxKws.png

A 10% damage increase would mean that it would roll to 3177*1.1 = 3494, correct?

But what about re-rolling damage? Do I need to find out how much my base roll could be improved by, and compare that to 10% of my current damage? So in this case, re-rolling a max base stat of 1788 would give me an extra 285. This is less than 10% damage because 285 < 317.7. Is that correct? Is the low part of the range not used in the calculation? And if so, is it because we assume that if the top end of the range rolls 285 higher, so will the bottom?

If this is correct, that means:

10% Damage Increase: 3177*1.1 = 3494 Damage
Reroll Main Stat: 3177+285 = 3462

So best case scenario they're about 1% within each other? And so the decision really comes down to how easy it is to get 10% affixes vs perfect rolls? And whether or not it's worth the sacrifice of another affix to get the 10% damage?

Do I have this right? Or am I completely off.

Thanks in advanced