Hey, so I set the world-ending biter level to be 5, as recommended, but I'm seeing biters up to level 7. I'm at 70% evolution, and I'm seeing a mix of level 5/6/7 biters attacking me, and nests usually have level 6/7 hives and worms

The initial and ending level in the settings affects health/damage/attack range.
The biters will always be from level 1 to 10, depending on the evolution.
So, if you set the ending level = 5 in the settings, then a level 10 biter will have 1000 health. If 7, then 3000. If 10, then 30000. Of course, this is base health, which can be affected by faction modifiers.

Ah, that makes a lot of sense. Thanks!