Not only modularity but it would also make occlusion and frustrum culling not being able to do anything with the not visible parts. It can only unrender whole meshes, not parts of meshes.
whats the frame rate so far and how many polygons so far and are you doing any blueprint Hierachical instanced static mesh system for the modular buildings?
I'm not sure what the initial problem might be, but could this possibly help --> http://hannesdelbeke.blogspot.be/2014/05/modular-arcs.html (especially the link to his Advanced Bend modifier) ?
Read up on modularity, your work is rather wasteful in terms of texture space. Here's a big thread with lots of stuff: http://www.polycount.com/forum/showthread.php?t=78444
Not a problem at all for this scene I made the modular texture first because all the props use that one Texture then I simply UV mapped all the objects to that texture.
You can always use skecthup for that ! as for max i guess setup your grid ( you need it anyway for modular enviro stuff right ? ) or use a helper such as ruler.
A modular piece for an environment I'm working on. Nothing too special, but I'm really pleased that I got some decent looking normals and lightmap specular inside UDK.
I'm working on a free indepth tutorial series on how to create the maya modular rigging tools from my site with python. Should be out really, really soon :)