Here's something you need to know (if you don't already... maybe I'm the last to figure it out). I have a 5,1 MacPro which started life as a 2.4Ghz 8-core, a pretty decent machine for audio, although I did occasionally wish for more CPU bandwidth. So I was pretty intrigued when i heard you could swap out the chips on a 5,1 with 3.33Ghz 6-core chips (and even on a 4,1 if you updated the firmware to make it look like a 5,1). The MOTUNation guys pointed out that you can now get a pair of these hotrod CPUs used, on eBay and elsewhere, for under $400. So I did. All reports made me expect a performance increase (as measured by Geekbench) of at least 50%. Here's what actually happened. Before: That multicore 64-bit score is pretty much the number you expect from one of these Macs. After: Holy cow! TWICE the multicore performance... a Geekbench score just a couple thousand points under the fastest current-model MacPro! You can feel the horsepower in even the simplest tasks (web surfing, even, is wickedly fast), and old DP projects that strained the CPU Meter open and run at a cool 40% of max. Insane value! A used 12-core 5,1 is going for something close to $2,500... with the Mac and the $380 I paid for the new processors, I don't even have half that in mine. Greater speed, bandwidth, four more slots for VI handling... whew! A couple of caveats: you do need some special tools - a kit of thermal paste (which increases contact and transfer of heat from the CPUs to the heat sinks), paste cleaner and surface prep (12 bucks on Amazon) and a 3mm hex key 5" long or more (to reach down inside the heat sink and loosen the captive bolts that hold it down). With these tools, I made the swap perfectly and confidently in 30 minutes, from gathering the tools to re-boot. Also, if you have a dual CPU 4,1 (not the single 4-core, the full 8-ccore) you will have to perform an extra, harrowing step: for some some dumb reason, Apple ordered Xeons with no IHC (integrated heat cap) for that machine, the only Intel Mac configured like this. So, after upgrading the firmware and removing the tray, you'll have to "de-lid" you new CPUs... use a razor blade and a lot of patience to remove the lid so the heat sinks can be tightened down completely without harming the CPU. But if you've got a 5,1, then No Jacket Required. This is the greatest no-brainer upgrade in the history of Macs. I am stoked/psyched/dead chuffed/delirious. Do it! Or bring it to my house and I'll do it!