I know its not the 8800 but i thought this was relevant:
Well my 2600XT radeon card arrived this morning. I tried copying in the x2000 drivers in case they worked with 10.4.11. Then I put the card in my 2006 mac pro & it booted fine (replacing a 7300) but the drivers did not load and the video was sluggish. Upgraded to 10.5 and they still did not load, upgraded to 10.5.1 and they loaded. I did later do an archive & install to fix a few things - as i would recommend to all, but the short answer is that the video is fine , overall performance is snappy but this is part due to the leopard upgrade & part the card. All i can say at this stage is that it works & feels fast. I will post an update when i have tried a few apps & woken from sleep a few times. If there are any particular tests people want let me know.
ATI Radeon HD 2600:
Chipset Model: ATI Radeon HD 2600
Type: Display
Bus: PCIe
Slot: Slot-1
PCIe Lane Width: x16
VRAM (Total): 256 MB
Vendor: ATI (0x1002)
Device ID: 0x9588
Revision ID: 0x0000
ROM Revision: 113-B1480A-236
EFI Driver Version: 01.00.236
Displays:
SyncMaster:
Resolution: 1600 x 1200 @ 60 Hz
Depth: 32-bit Color
Core Image: Hardware Accelerated
Main Display: Yes
Mirror: Off
Online: Yes
Quartz Extreme: Supported
Rotation: Supported
Display Connector:
Status: No display connected
Mac Pro Mac OS X (10.5.1)