From the Newdark guide:
Problem:
Low frame rate.
Solutions:
* Decrease display resolution.
* Disable multisampling ("multisampletype").
* Disable floating point render buffers ("d3d_disp_enable_hdr").
* Disable postprocessing ("postprocess").
* Disable "d3d_disp_sw_cc".
* Disable "d3d_disp_enable_distortionfx".
* Set "d3d_disp_no_rgb10_buf" to prevent the game from running in
enhanced 10-bits-per-channel RGB mode.
* If you're running with DX6 then try DX9 (set "use_d3d_display").
(Tweak these settings in your cam_ext.cfg file)