Concerning unit size and performance...

[Ciaran]

You could test it, RTW has more than one model per man, I think they come in four levels of detail. So you could try using only the models for the lowest level of detail (*unitname*_low.cas is their naming convention, I believe.) Just make the game use these cas files by editing the models_battle file.
Here´s an example:

model_flexi			data/models_unit/unit_egyptian_peasant_high.cas, 15
model_flexi			data/models_unit/unit_egyptian_peasant_med.cas, 30
model_flexi			data/models_unit/unit_egyptian_peasant_low.cas, 40
model_flexi			data/models_unit/unit_egyptian_peasant_lowest.cas, max

Now, to tell the game to use only the model with the lowest detail just replace the _high, _med and _low parts with _lowest. Maybe deleting those lines altogether, leaving only the last line might work as well, as some mods only use two levels of detail, but I´m not sure about that. Try at your own risk.

If the game runs significantly faster, that´s the solution. If not...

[EDIT]As everything I write about modding, this is a semi-educated guess at best! I haven´t done much of modding to be a save advisor, so don´t blame me if it doesn´t work.[/EDIT]