you may want to use expander as talked here or in config guide.
also look into better gpu. loose the ati and use 4000 as gui and have something beefier
for gpu. also look around here it is talked a lot.
also consider to have faster and cpu with more cores. weak machine will respond slower
and also will not be as good with red stuff.
you also may want to consider that maybe next year there will be new mac pro.
if your machine will be written off by then then it seems fine.
otherwise you may feel sorry afterwards.
some people build their system on win for that reason.
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Margus
http://iconstudios.eu
DaVinci 9, OSX 10.7.4
MacPro 5.1 2x2,93 24GB
GTX 470 / Quadro 4000
Multibridge 2 Pro