I am using Smoke with the latest Extension Pack and have a few playback issues. I can playback ProRes 4444 with a LUT in realtime without any problems. In another project I have H264 clips, but cached as ProRes 422 (8bit) and the playback is half realtime, so working appropiately is not possible. Debug mode shows me I have a lot GFX dropframes. But why don't I have problems with the ProRes 4444 clips? That doesn't make sense to me, as ProRes 4444 is the heavier codec to process and all clips are on the same drive.
I'm pretty sure caching still goes to an uncompressed file ie dpx, irregardless of what setting is used in the project file as this refers to intermediate renders, I may be wrong so happy to stand corrected.
As for the h264 problem, I have found caching on import to not always work for me so I turn off caching then apply a color correcter and hard commit it, this has been bulletproof for me so far.