"ATI 5770 Sapphire drop-in (2006) Mac Pro 1.1 (Dual 2.66GHz, OS X 10.7.5, 9GB RAM)
Just wanted to say after reading a user report not long ago on Accelerate your Mac, (PC Radeon 7970 in 2007 Mac Pro, or some other older post?) I found a used 5770 on Ebay (40 euro) so I thought I'd risk the used card to gain a bit of Photoshop and video app performance.

It was easy enough to drop in, just a bit harder seen that it takes up two slot widths. I first tried it in an upper slot and left the original Nvidia card in. Once rebooted I checked the System Report and it correctly saw the card as ATI Radeon HD 5000. I purchased a 6 pin Mac power lead from Ebay too. No problems there to install the power cable.

I then proceeded to swap monitors cables from the OEM card to the ATI. At first it was funky as monitor prefs was showing a third monitor yet was off screen. Clicking on any of the monitors though made it disappear.

Once I knew both DVI ports were working and could be interchanged I placed the ATI in the 16X PCIe slot. There is no start up screen as I knew there wouldn't be. (no Mac rom/EFI in card) I have since profiled (X-Rite i1 Profiler) the dual screens, no problems there at all.

The card runs very quietly, I've only noticed the fan once, yet was still quiet. Absolutely zero problems in any apps, and Photoshop recognizes the VRAM as 1024MB, thus fully exploitable GPU acceleration.

I would like to know if there is an advantage to run Netkas EFI 1.1>2.1 for the Mac Pro or if there is anything there for flashing the ROM with a custom BIOS also from Netkas. (was it a custom firmware or just a modified flasher (w/o model check) that allows 2,1 to be flashed into a mac pro 1,1? I thought it was the latter.-M) I've registered but have not yet been approved.

The Mac Pro is only used for graphics apps, I don't have time for video games. I did download Final Cut X Trial but it only runs on 10.9 Mavericks. I tried the SFOTT script and successfully wrote the installer to a USB 16GB key, but alas it says Mavericks can't be installed on this machine. I imagine that if the Mac Pro was updated to EFI 2.1 it may work.
Cheers, Neil"

Wish I was more help but if you like I can forward your mail to Davor who's running OS X Mavericks on his 2007 Mac Pro w/7970 Radeon card. (I think you saw his comments there already.) However personally I don't think I'd rely on Mavericks for a work machine yet, even on 'supported' hardware at this point.
   As for the 1,1 to 2,1 EFI update, netkas may have more info but it was said to correctly ID Quad-Core CPUs (in 2006 Mac Pros) and some said it fixed Kernel Panics they had after upgrading their 2006 Mac Pros with Quad-Core CPUs in OS X Lion (and 1 report on OS X 10.6.8 IIRC). I case you didn't see it earlier, here's a link to some earlier feedback on the Mac Pro 1,1 to 2,1 EFI updater.
  

• OWC posts 2013 Mac Pro Teardown Photos (thankfully still using socketed CPU)
• PCMag review of ($6799) 2013 Mac Pro (missed it earlier)
• How To Get Started with Lightroom 5 (Guide for Beginners)
• The best & worst 802.11ac Wi-Fi routers of 2013 (with six 802.11ac router reviews)

• iOS: How to transfer or sync content to your computer
• How to use multiple iPhone, iPad, or iPod devices with one computer

Thursday December 26th, 2013 News
• 2006 Xserve CPU Upgrade - Dual 3GHz Quad-Core X5365 (appx $150)
• 2013 Mac Pro Reviews Roundup/Recaps
• 2013: Apple's Year in Review
• Netgear ReadyDATA 516 review
• Updated Apple Support/How-To/Troubleshooting Articles:
  - Compressor 4.1: Fix for Opening to a gray window
  - Compressor 4.1: Troubleshooting Distributed Processing
  - iMacs: How to remove or install memory

For links to older news pages, see the Archives.