Civil 3D boost in performance.

    This simple boost in performance using Civil 3D 2015 & 2016 can help you finish your job quicker. The command CLEANSCREENON can save you plenty of time when trying to label or select certain Civil 3D objects when you are working in repetitive tasks.
    Let's say you have finished a pipe and pressure network and need to project certain parts into the profile and label some structures with different labels. Between picking a structure(s) you notice a delay before every command. This is a time when Civil 3D is using a lot of resources(RAM and writing/reading to disk) . In order to clear some of those resources to speed up your work you can use the command CLEANSCREENON. To revert this command type CLEANSCREENOFF.
Additionally, also run RIBBONCLOSE and to revert it just type RIBBON.


System variables to boost performance.
First, Use SYSVDLG to change the system variables. I'd also recommend creating a script to change these layouts to enhance performance. And to save the workspace settings and profile to further cement these changes.

Disable FILETABPREVIEW = 0
PURGE, remove all 'Regapps' (styles) not being used. Purge All.
If you are only doing 2D work (Top view) then turn off these two settings.
NAVBAR OFF
NAVVCUBE OFF
VISUALSTYLES
Edit 'Display resolution>Arc/circle smoothing to 100 (or lower if  you wish) I used 20
LINESMOOTHING OFF (this will make AutoCAD vectors look like Release 10.)