"Subject: MacPro 1,1 processor(s) and video card update
Finally got around to updating my Mac Pro 1,1 tower running OS X 10.7.5. I found a used PC Sapphire HD 5770 online for $75. I read that with OS X Lion these PC cards would work out of the box, and it did, but I did have to order the 6-Pin power cord separately off eBay ($7). Swapped out the 7300GT video card and plugged in the Sapphire card and it works great.
   One caveat, System Profiler recognizes the card as a HD 5000. I had read that since its a PC card it needs to flashed with a Mac EFI. (to show boot screen) Also, on boot the screen is blank until the login screen appears. My unscientific benchmark is that my boys are happy that Minecraft went from 30+ FPS to over 100 FPS. This card is very quiet.

For the CPU update, I did update the firmware to 2,1 using the Firmware Tool found on the netkas forums. (Earlier feedback on that in 9/19/2011 archives. IIRC must register for forums to get download unless it's mirrored elsewhere.)
   Found two Xeon X5355 2.66GHz Quad core chips for $70 for both on eBay, great deal. (Ref: Intel X5355 CPU info.) These replaced the original 2.66GHz Dual core Xeon X5150 CPUs.

Installing the new Xeons wasn't too bad, except getting the fan assembly out and re-installing it was a pain. I made sure to clean out all the dust and properly clean off the old grease off the heat sinks. Mac Pro rebooted fine and the processors were recognized correctly by System Profiler. Strange, but after five minutes the screen just went black. So I rebooted and zapped the PRAM and all was well now.

I did run GeekBench v2 on the tower prior to any updates and it clocked in at 4810. After the updates it scored a whopping 9167!"

I am pleased with the update! Just wish Apple would update the EFI so I could run Mountain Lion on this original Mac Pro!
(Some have worked around that (installing OS X 10.8 and even 10.9, past links on Macs/Mods page and here's a SFOTT (64 on 32) Applescript App bundle & (Rastafabi) Mavericks Install Guide for 32bit EFI Macs) but not sure it's worth it to everyone & some hardware/addons may still not be supported. Especially with OS X 10.9.0.)
Thanks for all info provided on your website, it has helped a lot over the years with my previous macs.
-Richard"

(Update: Here's a later report on a 2007 Mac Pro running OS X 10.9 with a Radeon 7970.)