Trouble with AVCHD in Premiere Pro on iMac Quad Core

Hello there,

I have recently upgraded from a Macbook Pro to an iMac, quad core i7 with 8GB of RAM. I have my AVCHD footage on a striped RAID hard drive connected via FW800 and the scratch disks on a separate 1TB hard drive that is not striped and that is connected via USB. I am using Premiere Pro CS4 to edit the footage.

When I play the video in PP, it warps on and off. It's better than when I was using my Macbook Pro dual core 4GB RAM, but it's still not playing smoothly. I have the presets set to 1080i30(60i), which is correct for this footage. The original footage was filmed at AVCHD 16M (FH) (1920x1080)

I would prefer to not have to convert the AVCHD footage, unless there is a clear advantage to doing this.I have tried converting to a P2 file, but it increases the file size from 284MB to 2.8GB.

Any suggestions?

Thanks,

David