Let me tell you about my experiences.
I had a maxed summoning tank. Back when BH worlds first came out, I was getting crap loot on my main. So I decided to try going pking with my summoning tank on them. Beforehand all I did was pk on PvP worlds because I thought they were incredible. So I take my summoning tank out to BH worlds, first targ kill I get 2m loot. The most I'd gotten on my main was 300k.
However, as my tank leveled up and became a higher and higher combat level, the loot got worse and worse. Here is my theory.
If you have a low combat level and high total level, you get great drops.
If you have a low combat level and low total level, you get crap drops.
If you have a high combat level and a high total level, you get okay drops, not too good.
If you have a high combat level, risk over 5m, have died with 5m before, AND have a high total level, you get good drops.
If you have a high combat level and low total level, don't even try BH worlds.