The installation was quick and without any problems. Computer on - old map out - new card purely - to computer - ... and running. Just ran the installation. Drivers under OS X 10.6.8 does not require. The map was immediately recognized and the picture was "like the old" card sharp.
Then the test came under Boot Camp. There, the Windows 7 system took first place high throughout low resolution. My Windows system was also, strangely enough, no hardware newly discovered, otherwise worked well. I came across the website of ATI and have downloaded and installed the appropriate driver for the 5-series. This driver Windows presented at the next reboot automatically preset resolution again, ie 1920x1080 pixels.
Although I have not made any benchmark tests, but I can say in relation to the original 7300 GT card, the speed difference is like day and night. "Chill" the card is at least twice as fast as the old one. Ran the simulation Train Simulator 2013 before more bad than good (you can actually say it was "not playable"), so it is now running smoothly and well. Light stuttering, there are still here and there, but only when really a lot of details have to be calculated. Normally it runs smoothly and without any problems. The fan on the map can not be perceived very low and under normal conditions. Even after several hours of Train Simulator it is still virtually inaudible and is drowned out by the fans MacPro-own.
For those who are interested here is the Windows 7 Pro Experience Index values my current MacPro:
Processor 7.2 7.9
RAM 7.2 7.9 (Note: The computer has 11 GB of RAM installed)
Graphics 7.4 from 7.9 with the new ATI 5770 (under the original GForce 7300 GT only 4.3)
Graphics (games) 7.4 7.9 with the new ATI 5770 (under the original GForce 7300 GT dwindle to 4.2)
Primary Hard Disk 5.9
With these values, my old 2006er MacPro is slightly stronger than the two-year-old office computer to my wife (also Windows 7).
So for me, the purchase is really worth it and I can get the card and to anyone who is looking for a replacement card. As has been written, the price is a bit higher than that of Windows cards, but you also have no trouble with flash cards etc.
Best Regards
Ludwig