Map Size?

[Romulator]

Whatever the POV of the player is focusing on will determine how great of a framerate loss there is. If the viewpoint has to process decals, particles, animations, entities and billboards, then there will be either a slightly or noticeable frame drop depending on multiple variables (pc performance, Amnesia settings, etc). Static_objects tend to obstruct the view, but do not always lower the performance of a large map, hence, looking down from the bottom floor will considerably lower lag if any since there is nothing to process, minus a Skybox or void.

A way you can get around it is to script "loading" areas. An example would be a script area between your floors and/or parts of the mansion, which will cancel out billboards, particles and decals which cannot be seen by a player between the floors or rooms. It will ease performance issues on both high and low end PCs, though it *may* create a bit of a spike when the script is triggered, depending on how many commands you need performed.

The map on its load will also be a bit laggy if objects need to "fall" into place, or "uncollide" themselves with others.

Personally, I would try not to make a really large map, but maybe a map for each floor and one for the front and outside (if necessary). It limits the amount of loading screens if you don't want them, but also provides reasonable performance leniency.