Trying to Edit AVCHD on CS6 and playback is choppy after 10 seconds...

Hi all

This is my first post on CC.net so here goes:

Trying to edit AVCHD 1080/50p .mts footage shot on a Panasonic SD90 and after around 10 seconds of playback it starts to get ridiculously choppy.

Editing on a 2ghz iMac with intel dual core 2 with 4gb of Ram. I'm guessing this is probably due to my machine not being up to the task so wanted to know what is the easiest way to edit these files via proxy and then replace them with the originals to keep quality high?

I have looked into Speedgrade proxy but they don't allow you to import .mts files.

Ive just changed from FCP back to CS6 because of the wide use of formats and really didn't want to have to convert files back and forth, wouldn't mind changing playback quality to 1/8 or even 1/16 to see if this helps, but cs6 won't let me get lower then 1/4 playback does anyone know why?

Thanks in advance.

Yannis