HI!
I could probably find this out with a bit of effort but i'm lazy so I'll ask it:
Do map entities render faster when they are compiled with high visibility settings?

Since you are incredibly correct abouth both you being lazy and able to find this out yourself, why don't you have a look at the manual, section "The A6 Engine"?
No offence. But it's really all in there.

I mean entities and not blocks if you think I mean that, but I couldn't find anything in the manual about map entities either!

I was also referring to map entities. With "manual" I meant the explanations of the BSP tree and culling etc. that can be found there. After having read those, you should be able to figure out yourself that map entities cannot render any faster with high visibility settings, since they are not part of the level's BSP (i.e. visibility) tree.
They are entities, i.e. non-static objects. As such, their visibility information is of no use to the engine since it can never know where the entity will be located.
Hope that helps, anyone please correct me should I be mistaken...