Lowering the resolution in Premiere makes no difference whatsoever unfortunately, even down to a 1/4 res, the lowest available option for the 1080p sequence.
It is a brand new raid volume. The only files on there are the image sequences. The raid volume is made up of 3 drives that had existing material on before, and I did a quick format of them when I made the RAID in Windows 7. So there are no cache files apart from the ones created on this single premiere project.
This new system has worked like a dream since I got it and I only invested further into a RAID to sort out the choppy image sequence playback, which is the only flaw, which is doubly irritating that it still unable to do it, even when I can get more than 300MB read rate from the raid.