Never seen Atum.
My experience with Twilight Forest was it was too safe. You could flee from the overworld and be in a place of peaceful calm contentment. Not in the theme!
Finally with the addition of Galacticraft I had to bump the memory some more. I don’t want the pack to be too fat, so I’m not sure I want to add any more major mods. I expect maybe small mods or tweaks from now on.