I have 150-200 malignant hearts, distilled fear, the blood and living steel having saved them up and now cashing in. I’m currently in T3 and have no issue with normal content but the torment bosses in T3 are completely different. However in T2 I steamroll them in seconds.
Is it worth the time to farm them in the harder T3 or should I just do it on T2?
I heard that the mythic drop rates are virtue same.
Never farm harder than necessary content. If you want to do it for fun or a challenge, sure, but not for farming.
You gain an extra 1% chance…for a mythic. If you need uniques, I’d go T3 or 4
Same situation as you, i farm T3 IH once i can handle the council for better Obdi drops.
So you want that unless you already MW max, since it’s double the T2 drop.
LB runs i melt on T2. GA’s I have gotten doubles on T2 and nothing on T3, so melting is always better imo.
if you want the “souls-like” experience have at it on T3.
But i wasn’t into farming mats so i am done, the cost per run seems to high imo. 
Edit- I got a ga unique on a T1-2 Boss so that versus the times i slogged a T3 wasn’t worth it, same for IH loot. Since a run on any level can give bad rng, its just better to melt and get more chances. Unless you are feeling lucky, well do ya, feel lucky
The higher in torment you go,the more uniques bosses drop and thus a higher chance of an ancestral unique. T1 bosses only drop two, T4 drop five.
And as mentioned, mythics have a slightly higher chance of appearance.
You are better off running against T2 bosses. Less drops, yes. But you can power through boss runs quicker.
Only do bosses on T4. You can always find a carry person if you are not strong enuf. This gives you the most chances at good loot.