The other fights have higher NOTHING chances.. Of course rakvar is the most challenging fight of the bunch hence putting his nothing amount a lot lower...
Well thats one of the points i was trying to make earlier, with higher no-drop chance on the other bosses its going to take longer to get those Soulstones, Rak'var takes 2:30-3:30 if i dont die, if i die it can go up to 5 mins, even tho the Warlock isnt as Hard, i still die sometimes on that fight AND you have to kill the Executioner which takes 2 minutes to kill (almost always 2 mins exactly
So the Warlock actually takes longer reach and kill than a single Rak'var, and the Warlock also has 3x higher No-drop chance, im mentioning the warlock since i got hes Soulstone yesterday and it was the HP one, so i know who we will have to kill to get a larger HP ppol (which is the most important thing for DF now after you cap defensive stats).
For my computer it takes about 38-42 seconds to load a new game-go to portal-load in to DF.
Troll King: 1:40-2min
Double Dragon 1:40-2min
Dragon Rescue: 3:30-4min
Executioner: 2mins (Exactly 2 min on the second most of the time
Warlock: 2:00-2:30 (Usualy takes about 2 mins if i dont die, then it takes a little bit more time, up to an extra 30 sec)
Rak'var: 2:30-3:30 no deaths (up to 5 min if i die)
Abe: Not sure, hes boring, too much Missile Reflection so havent done him so much
Netherlord is going to be the one that takes longest to farm Soulstones from because it takes ~5 minutes to reach the Nether Realm, so about 6-7 minutes to kill him, thats almost twice the time it takes to kill Rak'var, hes no-chance weight is also higher which makes it really painful trying to gather soulstones from him.