HD Video Export Bottleneck

[zachsilvey]

Here is the setup:
Exporting 720p video in H.264 from Final Cut Express 4 on a MacPro

Specs:
2x2.66 dual core Xeon (woodcrest)
2 Gb RAM
4x1 Tb drives in Raid 5 (raid card)
Nvidia 7300 gt

When exporting video I am getting large valleys in the cpu usage graph, I have a feeling I am hitting a bottleneck on either the ram or the drives (cpu usage graph attached). Has anyone else experienced this on a similar setup? If so what do you think the bottleneck is.

 

[zachsilvey]

Update:
I found out that the raid card hadn't finished initializing the 2.6 tb raid 5 volume (it ended up taking about 36 hours) and during that time the read and write speeds were greatly reduced. I retried the export after the initialization was completed and it seemed to help but now it seems that the ram just isn't cutting it. It looks like it is time to jump to 8 or 16 gb.