After countless problems with playback issues in Premiere I spent some time looking into what might be causing the problem on my system and it just seems like the way Premiere is handling cacheing is messed up.
As an example if I load a bunch of clips into FCPX throw them together in a timeline and hit play then watch my RAID I can see a steady read rate of around 50 MB/s. If I add more layers then the read rate goes up accordingly but the playback stays smooth because my RAID can deliver content at up to around 500 MB/s.
In Premiere Pro CS6 however it's a different story, the same process results in what looks like very random access to the RAID. Premiere seems to load footage into some kind of cache (RAM Buffer?) and then call up content in blocks as and when required. On my system this results in random read sessions up to 300 MB/s followed by a few seconds of inactivity from the RAID.
Whenever playback suffers a stutter or locks up it's usually just before one of these high speed reads which leads me to think that premiere is requesting the data in advance of the timeline needing it but it's arriving too late to keep the playback fluid.
I can't help thinkign that the simpler approach of streaming in the data as required works much better.
Mac Pro 12 core / 48GB Ram / SSD Boot Drive
SAS based RAID Storage