Where possible you may be able use MDL files for many of the details - at least test this out - I have found a great number can have little effect on frame rates - world geometry not so. Many detailed railings or fences, gates etc for instance have little effect on frame rates.

Textures also have a major impact - though I would not dare suggest you alter any of those shown in your screen shots which are excellent and a credit to you. If its a last resort you can increase frame rates dramatically by rescaling/tiling textures which may need to be seamless in some instances - though a decrease in quality results so you would obviously start with the least seen ones first.

Your buildings are certainly detailed and from what I have seen although you have great detail I would not have thought that the views shown would have caused unacceptable frame rates. If so then your scenes are more complex than can be asceratined from the screen views.

Obviously you are attempting a somewhat no compromise quality approach to the levels and that is to be commended - in reality though I beleive GS to be by comparison the best FRate engine in its class you may be asking just a little too much of it.

I hope not as we want to see much more of this.

Keep up the gret work