Mac Pro 4,1 Processor

http://www.everymac.com/systems/apple/mac_pro/faq/mac-pro-early-2009-nehalem-how -to-upgrade-processors.html

All "Early 2009" Mac Pro models have the processors mounted on LGA 1366 sockets and Apple did not impose any firmware restrictions, either. However, as is common with Mac upgrades, significant hurdles apply.

http://eshop.macsales.com/shop/turnkey/MacPro/2009_2010_Xeon_Processor/Apple_Mac _Pro_2009_1

http://www.xlr8yourmac.com/feedback/2009MacPro12CoreCPUupgrade.html

http://forums.macrumors.com/showthread.php?t=1836888

2009 Mac Pro Dual 3GHz X5675 CPU Upgrade (12-cores)

Processor Upgrades

http://forums.macrumors.com/showthread.php?t=1333421

Many Users of Mac Pro are surprised to discover that their Mac is not compute-bound, but has many extra cycles already. Unless you took steps to fix it, your Mac is likely I/O bound around the "everything" drive used for Booting and all the files. Be sure to use Activity Monitor to check that your Mac really doe not have any more CPU cycles available, or you could be fixing the wrong stuff.

User Tip: Creating a lean, fast Boot Drive

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Do you have the low end 2.26? If you could not find anything then probably not a good candidate for doing so.

If you have the low end MHz model, even 3.2GHz 8-core would give a significant boost.

Anyone and everything thing gets a good boost from SATA 3 and above, from 550MB/sec SSD to 1100MB/sec XP941 blade.

(I have one heck of a time with my browser editing links in forums in the last year, sorry for bad links)

Did you notice http://www.xlr8yourmac.com today had articles?

(These are NOT links just how this forum deals with copy/paste and makes them look so. )

2009 Mac Pro Dual 3GHz X5675 CPU Upgrade (12-cores)

Another 2009 Mac Pro NB (overheating) Heatsink Retainer Repair

2009 Mac Pro 6-core 3.46GHz CPU Upgrade, Repair NB Heatsink Retainers

2009 Mac Pro 12-core CPU Upgrade (Dual 2.93GHz X5670 Westmere CPUs)

2009 Mac Pro Northbridge High Temperatures? Check Plastic Heatsink Retainers