This is not if you have bad hardware. These are instructions for people who are experiencing worse performance than they should be.

Type "p_logall" without quotes in the console (~ key) whenever you want to begin recording in game (don't do this until you at least spawn in a round)
then you can p_endlog /or just wait for the round to end/ or map to change/ or just quit the game and it will end automatically.

Then navigate to your hidden folder
c:/users/YOU/appdata/roaming/natural selection 2/
And you will find your file, something *.plog
Zip it/ compress it.
Upload it to somewhere on the internet
Make a thread in the tech support forums, and put a link to your .plog file there.
In the thread explain why you think you are getting worse performance than you should.

This will give UWE a frame by frame analysis of what is going on, so try to pick a time when you can best reproduce your lowest performance like the 24 fps you said you get.
Don't record for longer than 30 minutes, and don't record for shorter than 5.

Include your file with this compressed plog.

Link to the UWE techsupport forums.