One of the big time killers with Civil 3D comes from data management overhead. A lot of time goes into configuring and manipulating management schemes to be able to work efficiently. The site topology paradigm in itself is a pain to work with, not to mention style managment, data shortcuts, etc.
The system requires a lot of pre-configuration to work efficiently and accordingly it does not readily adapt to scenarios that are atypical of the standards it was set up for.
Infrastructure Suite/C3D 2013, LDT 2004, Power Civil v8i SS1
WIN 7 64 PRO
HP Pavillion h8xt, i7 2600, 12 GB
RADEON 6450, 1 GB