Will the ati 5770 work with my 3,1 Mac Pro

Apple does not recommend what they have not tested extensively.

They do not test out-of-production computers again for anything.

So they only recommend that newer card in current equipment.

Your friends here at the Apple Mac Pro support community can assure you that the Apple brand ATI 5770 card works just fine in your machine with no known issues, The drivers are in 10.6.5, so you will need to update to at least that version.

If installing in an even older Mac Pro that only has PCIe 1.1 support, the card works fine but is slower that its benchmarks would suggest becuse of the slower PCIe Bus.

Graphic wise, there isn't that much difference between 2008 and later other.

You have PCIe 2.0 support so bandwidth is fine.

Barefeats.com did a lot of tests.

Apple has this strange policy of not really supporting prior hardware models or older OS. In this case though, esp. for a "non tech" like yourself, I think you jumped the gun on Lion.

https://discussions.apple.com/thread/2571648?start=15&tstart=0

http://www.barefeats.com/wst10g4.html

The only thing Apple has to say:

PS: Apple Community editing replies in IE9 is just plain broken, terrible and the worst experience. No other site, forum acts this bad. Gotten worse, much worse, than it was before. AD worked. Safari has its own problems, still isn't multithreaded and smooth, and causes other problems.

This is just a test with IE10 Windows 8

Mac Pro: Using ATI Radeon HD 5770 graphics card with Mac Pro released before 2010

You may notice display anomalies or issues playing back video or other HDCP-encoded content when you use an ATI Radeon HD 5770 video card in Mac Pro computers released before the Mac Pro (Mid 2010

http://support.apple.com/kb/TS3891

Looks just as bad; not sure what Apple is using.

I have been using the ATI Radeon HD 5870 for a year now and have NEVR had one single issue... this card is flawless in a 2008 Mac Pro 3,1 and plays anything game wise I throw at it...most all games on max settings (F.E.A.R. 3, Call Of Duty, Left 4 Dead 1 and 2) Plays DVD movies perfect as well

This card also works the exact same in Windows 7 64 bit and you can even stick it in an actual Windows machine (non boot camp) and it just simply flies! 🙂

That is a $200 question that I'd say go back to Barefeats and look.

And also see what is brewing on http://netkas.org

Yes it works without any problems, I have same configuration and it works great!