Models or entities in large outdoor level?

I'm working on a 3D reconstruction of my home town in the 17th century. I will need around 200 buildings and I've completed about 90 of them. All built as entities in WED and incorporated in the city-level. Apart from these I'll need town-walls, gates trees people and a lot more.

Recently I got help from a couple of students from a nearby game-development school. They do a thesis by adding game-play to my - rather static - level. And they advise me on performance issues. Recently one of them commented that my way of building houses using was not very efficient, because I was using too many invisible polygons en too much textures. In fact I should switch as once to real modeling!
Is he correct? I Think a make simple entities, look at this link for an example.
It is a fact that my framerate is dropping while adding more entities to my level. Are entities so inefficient that I should switch to modeling?
Please some expert advise!

While it is true that simple modeling like this is adding unseen faces and such, it is unlikely that it will affect performance as much as I think they're making it sound. Gamestudio uses an effective culling algorithm that does not render unseen geometry.

Instead, your performance issues are probably related more to the fact that the simple modeling is using more video memory. More shapes take up more space. If your intended user is like to have a high-level system, this shouldn't be a problem.

There is a trade-off here: simple shapes tend to be easier to texture, both for you (the creator) and the computer (the renderer).

My recommendation is to try making a few "complex" models and compare them to your simple models. There's a couple of things you'd probably want to consider:
1) Am I getting a noticeable performance increase?
2) How long is it taking me to make these new models? Is the extra time worth the gains?
3) Do the models look good? Are they matching my intended style? Are the textures looking okay?

See how things go. Looks good otherwise!

(Edit) Sorry, I saw something else I wanted to address. As long as you are using the same textures repeatedly, there shouldn't be a performance decrease. The texture images are loaded in the video memory once, then used over and over again on the models. Again, this might be another reason that simple modeling is good, since you do not need an individual texture for each model.

Thanks JMichalc for your reaction.
I agree on you first comment, a trade-off must be considered between fast, cheap, less detailed entities and more time consuming and more detailed models. I'm now setting up a comparison. The problem now is that until now I had the impression that the fast-and-easy-way of building entities using the WED seems to be the least efficient way in terms of system resources...
Am I correct in this assumption? I hope someone can convince me that I'm not!

With respect to the second part of your answer:
Is it correct that textures are only loaded once into video memory?
My students maintain that I should reduce texture size and number of textures.

At this moment I use for every house one specific texture for the streetfacing walls, the other walls, roofs etc use standard textures. Adding all texture sizes and rounding them upwards, results in a total of 200 Mb for textures. Is this an excessive amount?
The textures for the streetfacing walls are bmp's, mostly 512x512px and 300 dpi. I selected this combination by comparing different combinations of size en resolution for best rendering.

Any comments on these numbers are welcome!

I am one of the students asu was talking about, and if I had read what he said I would have agreed with you as well. but he didn't state what the true problem was. the problem isn't as much the fact that his buildings are showing extra faces etc. altough some of them are 2 times as big as they need to be since the half of the pollies are invisible.
but that isn't as much the point as this.
like he said they finished around 90 buildings. and all 90 buildings have their own texture, since they want every hous to be difrent and are using no window or door objects they are doing this with textures.

so this means they have 90 textures of 512 x 512 x 300 dpi alone fore the front of the houses, then 10 defrent textures fore the ground alone also all 512 x 512 x 300 dpi.
then about another 20 of those textures fore the sides of the houses again 512 x 512 x 300 dpi. and then 5-8 512 x 512 x 300 dpi textures fore the roof.

with a few calculations done by asu him self the textures alone will taake up 200 mb's of space alone when the city is done.

this is with out the 200 buildings, wich are all unike so that means 200 houses need to be loaded in not counting the gates and walls.

then there are all the other things like stones and trees, wich are done efficiant and I have no problem with those.

and afther all that we need to put in our own models to make the market interactive not to mantion a few small game events.

so to sum it all up, it's astimated that we will have the folowing when the program is finished with out even adding the game element.

- 250+ textures of 512 x 512 x 300 dpi
- 210 buildings of 60 - 120 pollies each
- a couple of extra objects
- 1 moving moddel with her own textures
- and more random stuf that isn't seposed to be there

and I'm sure you would agree that this is just way way way to much.

ent_purge may solve your problem

how exactly would that fix our memory problem.
I mean we would still have all of the textures not to mantion all the other stuf that isn't seposed to be there