Mick,

Hold On! Before you get an x1900 consider this. x1900 is for the pre 2008 machines.

If you are buying a new Mac pro and you haven't gotten it yet, you will be buying a generation 2 Mac Pro. For the gen 2, the best card is the 8800. Gen 2 Macs also are 8-core by default so don't step down to the single processor 4 core because it's not worth the savings.

I have one of these machines now and it is running two TripleHead2Go devices and is outputting 6 screens 1024x768 at 75Hz or 6 screen 1280x1024 at 60Hz.

It works for me, is rock solid, and with the two ssd disks, I am running 16 layers with issues.

Oh, and make sure you run all the Leopard Updates. Before I did the graphics update, my box was only running half as many layers. Also make sure to go into quicktime settings and enable legacy codecs.