Yes, I would transcode AVCHD footage to a more editing friendly codec if you want to continue using CS4. The problems you are having with the GH1 footage are going to be the same with the HMC unless you transcode (convert to another codec) for editing. If you want to upgrade to CS5 then things apparently get much easier, but there is a cost involved in doing that.
You should also be transcoding your 60D footage too, because trying to edit (in CS4) with native AVCHD is going to drive you crazy.
You should also be transcoding your 60D footage too, because trying to edit (in CS4) with native AVCHD is going to drive you crazy.