Honestly, I registered just for this project. This is fantastic work, minus the fact that performance is terrible

. The subway area to me, interestingly enough, appears the most detailed.
My suggestions and comments are mostly obvious ones:
1) There appears to be a ton of overlapping lights, which reduces framerates and causes a sortof "glare" in spots of the map.
2) I noticed afew of what appeared to be "light leaks". You may want to check that out.
3) Turning the lights on and off seems like it may be causing problems, especially that given lights may not always be turned on or off properly. I'm sure this can be fixed up though.
4) Obviously, visportals need liberal use in this map. The biggest problem here involves building interiors. But you could modify the windows of buildings to have an environment map type reflection normally, and otherwise be opaque. As you get closer you could "fade" more transparent. This may work. The brush idea someone mentioned is another possible fix.
One thing I noticed is that this build appears more "washed out" than the previous one. Not sure why. Overall very nice though, despite the framerates. Even though I knew my machine couldn't handle it, at one point I knocked it up to 1024x768 with 4xAA, and it was quite stunning, even if I was getting 1fps. As I told a friend "It may have been a slideshow, but it was one of the prettiest slideshow's I've seen."
Oh, the other thing I noticed, I should mention, is sometimes objects get "stuck" for instance I was able to get a chair stuck on a window just by throwing it at one (in the embassy), and was able to repeat this afew times before it finally decided to fall normally. Also I tossed a ragdoll around and it actually got stuck on something in the air at one point. Then (yes another), in the subway I tossed a guy in with the janitor, killing them both, and one of them (I think the janitor) somehow ended up stuck with his arm in the wall by the stairs. He was not able to be removed from that spot (though I could flop him around a bit). These errors may denote leaks and other sorts of problems rather than actual physics bugs. Who knows.
Good job though guys. Can't wait to see more.