I've been trying out the new free version for only a few days now, but so far the best codec to use for editing for me has been the free GoPro Cineform codec that gets installed when you install the free GoPro Cineform Studio application. So you will need to transcode your footage outside of Lightworks (my codec swapping utility does not work with the new version). For lossless transcodes you can use the UT Codec Suite or Lagarith.

From the tests I've done it seems that any codec that Lightworks imports through it's Mainconcept plugin system is having performance problems. Even Matrox MPEG2 I-Frame HD that used to work flawlessly in the beta has problems (stuttering, freezing when stepping) now that it's being decoded by the Mainconcept plugin. Devs, please look into this.

Have just installed LW11 over my LW beta and the new version works flawlessly (including my Shuttle Pro V20 setup!) I used the free 'DSLR Post Prep' to transcode my camera's AVCHD .MTS files to the M701 codec which was optimised for LW beta. I'm pleased to report this codec also works very smoothly in LW11, even on my low spec Windows 7 i3 laptop!

PS: DSLR Post prep also allows transcoding to DNxHD codec (license required for LW11)

I'll have to look into this more. I have some directshow filters (halii splitter, lav filters, etc.) that might be interfering with the Mainconcept plugin system Lightworks now uses.

With the Go Pro Cineform Studio I get erratic fps readings. When I import a clip it can say anything from .23 fps to a wopping 960.00 fps!! I tried this app before I read your post and was going to dismiss it. The result is it will render the video into mega fast or slow, with split second to endless render times to match.
Any advice?

Can anyone help with this?
Is Cineform Studio an acceptable codec conversion solution?
Tips, tricks, help please.

Cineform Studio's main use is for GoPro Hero video files. Other sources aren't guaranteed to work. What's the source of your variable frame rate clips? To edit your video you will most likely need to convert your clips to a constant frame rate. I don't think any NLE can work with VFR video files.