This is actually quite normal. FC is an awesome plug-in, but slow as hell to render.
I've taken to pre-converting my H.264 footage to DNxHD with the FC settings 'baked in' via LUT. This has two advantages. First, DNx edits waaaaay better than H.264, and second, with the FC settings baked in there's no need to apply the plug-in. (And in my testing, adding the effect via LUT during pre-conversion actually goes a LOT quicker than adding it to the clips in the sequence.)
One caveat, though. All the settings from FilmConvert will come along with the created LUT, except grain. If you want grain, you will still need to apply the plug-in to the sequence. But at least this can be done at the end so there's no strain on the system while trying to do color correction and grading.
Thanks for the reply. I'm still in infancy when it comes to pre-converting footage, etc. so I just stick with H264 at the moment ... but I have discovered something. I use a GH4 and shoot in 4K. Usually I drag the 4K files into a sequence and then resize the sequence to 1920x1080. This improves editing performance and let's me export 4K downscaled to 1080. It seems FC doesn't like this approach though. If I leave the 4K sequence as is, I can get an export of 1.30mins of 4K footage with FC applied done in ~7.30mins. If I downscale the 4K sequence to a 1080 sequence and export in 1080 with the same FC settings applied, it takes up to 50mins. I don't really understand this, but there you go