HD video "chugs" in fcp7 and I cant work out why

Hi,

I edit 5dmk2/60d/550d footage ( lots of sliding and complex moves) in fcp7 naturally I convert the footage, I use Apple XDCAM HD 1080p24 converted via stream clip.

the converted files are placed on a sandisk 240gb solid state drive and then imported to fincut which has its render/prodject /scratch folders set to same location. ( i only edit one project at a time with about 60GB to spare)

the computer is

Model Name: Mac Pro
Model Identifier: MacPro4,1
Processor Name: Quad-Core Intel Xeon
Processor Speed: 2.66 GHz
Number Of Processors: 1
Total Number Of Cores: 4
L2 Cache (per core): 256 KB
L3 Cache: 8 MB
Memory: 12 GB
Processor Interconnect Speed: 4.8 GT/s

I have trim enabled on the ssd's

I have system files running on 120GB sandisk SSD and the usser files on the WD 640gb 7200rpm disk that cam with the mac.

I also have a external 4 disk raid5 which i achieve my media on...with space available if this will help in some way.


Thanks for your help.