If you want to k ow how to caculate it…
149% vs 137%:
Understand that the increase to damage, although multiplicative, is additive to the 100% base damage you can do without it. So we add 100% to both for 249% vs 237%. Now we devide, 249/237=1.0506. The answer is now in decimal form, convert it back to % by multiplying by 100. 1.0506 x 100= 105.06. Now we subtract our base 100% to calculate the multiplicative damage difference. 105.06%-100%= 5.06%. So the 149% value is only actually 5.06% more damage than the 137% value. That is just comparing the legendary stat value.
The offhand WD item also grants additional damage range. An ancient legendary can have higher values. To calculate the multiplicative value of that difference you need to grab the white damage range at the bottom of your weapon then add in the offhand damage range plus any other damage range stats you may have from rings/necklace. Add up all of the lower range values, then add up all of upper range values. Once added, add the total lower value to the total upper value and devide by 2. This gives you the average. You will not always hit for the higher number. Do this for both items, then devide the resulting 2 numbers. This will be the decimal value of multiplicative difference.
You do not actually have to do the math for the damage ranges, as swaping between the items will affect your sheet dps. Doing this also accounts for differences in mainstat, crit chance, crit damage, and attack speed. Just swap between the two items and check your sheet elemental dps. Cold I imagine. In the sheet details it will give you a elemental dps number. Compare this number between the two items by division.
If item one gives 149% with cold elemental dps of 4,362,880 and item two gives 137% with Cold elemental dps of 4,577,231 then:
149% item gives 5.06% more damage from legendary stat and 137% item gives 4.91% more damage fron dps. The winner in this case is the 149% item.
Of course you also have to consider damage increase from potential augments. Each augment level is worth 5 mainstat. Look at your mainstat between the two items, calulate what your mainstat will be with each. Divide the larger number by the smaller number.
Say the 149% item in non ancient, and the 137% is ancient. One could easily say the ancient item will surely have 200 more mainstat to start with. If you augment with a 120 gem (120 x5 = 600) you would gain 800 additional mainstat by augmenting and using the ancient. Lets say you have 25k mainstat with the non ancient, you’ll have 25.8k with ancient augmented. 25.8/25= 1.032 or 3.2% increase in damage.
If we then apply that to the before calculated numbers of:
Item 1 with 149% at 4,362,880 and 25k mainstat
Item 2 with 137% at 4,577,231 and 25.8k mainstat.
Item 1 would get 5.06% more damage from legendary stat.
Item 2 would get 4.91% more damage from dps and 3.2% more from mainstat. Convert the % back to decimal to calculate combined damage increase. 1.0491 x 1.032 =1.0827 or 8.27% damage. Compare the 5.06% from item 1 to the 8.27% from item 2. 1.0827/1.0506=1.0305%. So in conclusion, item 2 with 137% stat actually does 3.05% more damage that item 2.
These numbers are obviously not the numbers you have.
Sometimes, a 137% stat can be better that a 147% stat. Just have to do the math.