most people that keep the dual 867 nice and cool have great experience with it.  some say that 58c/135f is normal for all the dual MDD but its not healthy.  shame on apple for putting them out there like that when they could have easily made it run much cooler like I have.  besides..  my dual 867 is a later model that used underclocked 1ghz chips.

I honestly notice the system having less lag and in general it seems more precise now.

from the research I have done the pci exhaust fan i'm getting soon from ebay will lower the temps by a minimum of 8-9c.  so when all is said and done the cpu board on my mdd will be around 40c/105f.  thats cooler than single G4's

many people have dual 867 mdd..  they were by far the best selling mdd of all the speeds.  it sold so well that they continued to make the dual 867 when the rest of its series was discontinued.  ie when the fw 800 models came out.  you are the first person I have ever heard of having a bad experience with them.
Mac mini C2D 1.83GHz - 2GB RAM - 200GB 7200rpm HD
Sawtooth w/G4 1GHz - 1GB RAM - SIIG SATA w/2x1TB HD
B&W w/G4 600MHz - 1GB RAM - 2x80GB HD
Sawtooth G4 400MHz - 512MB RAM - 40GB HD
Dell Ultrasharp 2007WFP 20" Widescreen LCD
2.94TB Total Storage