Michael,
I use Compressor 4 and my GoPro and have found that Compressor 4 is more efficient in the set up and use of multiple cores/ clusters etc.
The UI is much the same as Compressor 3 – which could be a good point or not, depending on how you are sitting on your chair.
The integration between FCP X and Compressor 4 is better – though that is a personal comment.
Ingestion of GoPro mp4 into FCP X goes smoothly and without a hiccup, in my experience.
That’s all I can say as I’ve never had to think about it, personally.
Regards,
Lawrence