Although many have wanted to either dismiss or refuse to acknowledge this issue, Apple continues to have major problems with it's Nehalem chipset:

Apple acknowledging, investigating Mac Pro problems? | MacNN (http://www.macnn.com/articles/10/02/09/temporary.workaround.requires.extra.hardware/)

Although I often work with third-party developers to help rectify global issues this one in particular is something Apple has been keeping close the their chest.

The caveat is that with the soon-to-be-released new hardware releases from Apple - along with how they choose to finally address this particular issue - it would be very wise *not* to make any investment in Nehalem-based hardware until either they find a global, proven fix to this problem and/or wait for the new "next-gen" hardware to be released and see if it too suffers from the malady.

Caveat emptor, my friends.

Apple Releases Software Update Addressing Audio-Related Mac Pro Heat and Performance Issues - Mac Rumors (http://www.macrumors.com/2010/02/11/apple-releases-software-update-addressing-audio-related-mac-pro-audio-heat-and-performance-issues/)

Even though they fixed the audio issue, I still feel a processor update is imminent. And by imminent, I mean the 6-core Gulftown server-class processors. While it might only replace the high-end configuration, I see the 8-core 2.26 being hacked off the store selections and filling the refurbished area with a big discount.

Am waiting anxiously for the 10. My hope is for a little better bang for the buck. Base model faster than the imac and please more than 4 ram slots. It kills me to think that the first thing that you do when you get your new comp is to trash 3 brand new rams. It'd be nice if you could pop a few more gigs in there & get at least a few months out of the supplied ram.

Since they seem to have a fix, an 09 8 core would work.