wow, you know your map archive made me realize, i do not do ANY of the epic exploratory mining that was necessary in 40d anymore. ore is just so readily available, and if you hit the caverns all you need to do is walk around and check the walls for what you want.
im not sure whether i like that or not. i can now understand why my miners are constantly idle in the current version. in 40d they were allways out looking for more ore, gems and coal. now its much easier to find.
your circle-fu is pretty nice. try and take the same concept and get more epic with it. also, most of the tilesets now have the smooth round edges thing going, so try out those. also, did you designate by hand, or with a program?
i went a little nuts with the central circle idea in what is probably my largest fort -
http://mkv25.net/dfma/map-5254-friendlyworkscheck the lower living and storage areas. i went pretty crazy there, had to housesit a friends place for 2 days to keep their pets from dying, and had not much else to do. everything designated by hand, and all slightly asymetrical as a result.
other option is to attempt some kind of very large aboveground construction. best to embark on the edge of a mountain and let the terrain inspire you. some kind of tower, or bridge, or castle. also, i have yet to see any good megaprojects involving the caverns, although im sure there are a few lurking around on the forums.
and browse the map archives. i allways find whenever ive done something i feel proud of, i find something on that site that floors me and puts me to shame. its a great place for getting ideas on completely new ways of laying out a fortress.