2.7.0 updated support for those processors; actual support was added in BIOS version 2.0.1, wherein you will find: ************************************************************************  IMPORTANT NOTE************************************************************************ This release is the first customer release for Systems labeled 'III'.* * The following features are supported for systems labeled 'III' only.** Added support for Quad-Core Intel(R) Xeon(R) Processor 5400 series* Added support for Trusted Platform Module 1.2.* Added support for Internal USB storage.*********************************************************************** [URL] And the following in the Information Update: • If the front of your system chassis is labeled with a “II”, your system isupgradeable to the 5100 series of dual-core Intel Xeon processors andthe 5300 series of quad-core Intel Xeon processors.• If the front of your system chassis is labeled with a “III”, your system isupgradeable to the 5100 and 5200 series of dual-core Intel Xeon processorsand the 5300 and 5400 series of quad-core Intel Xeon processors. [URL] Line:Revision I: 5100-seriesRevision II: 5300-seriesRevision III: 5400-series 
OK I've just about had it with upgrading the processors in this server.  I have updated the BIOS to 2.7.0 in which the release notes say: DELL INC.BIOS RELEASE NOTES~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~System:         Dell(TM) PowerEdge(TM) 2900Version:        2.7.0Release Date:   12/03/2010______________________________________________________________________* Updated Dual-Core Intel(R) Xeon(R) Processor 5100 series B2 Stepping Microcode (Patch ID=D2)* Updated Dual-Core Intel(R) Xeon(R) Processor 5100 series G0 Stepping Microcode (Patch ID=BC)* Updated Quad-Core Intel(R) Xeon(R) Processor 5300 series B3 Stepping Microcode (Patch ID=6B)* Updated Quad-Core Intel(R) Xeon(R) Processor 5300 series G0 Stepping Microcode (Patch ID=BC)* Updated Quad-Core Intel(R) Xeon(R) Processor 5400 series C0 Stepping Microcode (Patch ID=60F)* Updated Quad-Core Intel(R) Xeon(R) Processor 5400 series E0 Stepping Microcode (Patch ID=A0B)* Updated Dual-Core Intel(R) Xeon(R) Processor 5200 series C0 Stepping Microcode (Patch ID=60F)* Updated Dual-Core Intel(R) Xeon(R) Processor 5200 series E0 Stepping Microcode (Patch ID=A0B)~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ So I purchased 2x 5420 Quad Xeon 2.5ghz processors stepping C0.  Clearly on the list above.  After install received "Unsupported CPU Combination" blue and yellow blinking on boot. So I dug a little deeper and found that only the 5100 and 5300 series processors are actually supported.  So I promptly purchased 2x 5320 Quad Xeon 1.86ghz Processors Stepping B3.  Received and installed them only to receive the same blinking "Unsupported CPU Combination". Luckily old xeons are cheap on ebay so I'm not losing my ass here, but c'mon.  WHAT is the best processor pair I can put in this server!?
What is the maximum supported processor for the Dell 2900 (Gen1)?