Lots of people have to slow down their video cards by limiting them to AGP 4X. Usually their problems at AGP 8X aren't as severe as yours but I've seen peoples' monitors go into standby mode at AGP 8X. For most folks (including me) AGP 8X just causes the occasional crash. The actual performance loss of running at AGP 4X is at most a few percent and in most circumstances much smaller than that so don't worry about the performance.
The performance loss of disabling fast writes depends on the video card and most aren't measurably affected. I'm pretty sure that the Radeon 9600XT is one of the cards that is affected by disabling fast writes but I'm not sure about a 9600 Pro. You should leave the AGP speed at 4X but you might try to see if it runs faster with fast writes enabled. You could use 3DMark as a benchmark to see if it matters. Slowing down to AGP 4X is enough to solve most peoples' problems so disabling fast writes usually isn't necessary. But since it has a negligible effect on performance on most cards people just disable fast writes because they have a reputation for causing problems.
ATI drivers have a built in AGP tester called SMARTGART which can automatically find the fastest reliable settings for your AGP port. So even though AGP 8X and fast writes are enabled in the BIOS you can still end up only running at AGP 4X and fast writes disabled. It may have worked in the past because SMARTGART had slowed down you AGP port without you're knowing it. It's supposed to do all the testing automatically but its tests are so short that it often misses transient problems. SMARTGART's tests don't catch all problems so they allow you to manually limit your AGP port properties.
The performance loss of disabling fast writes depends on the video card and most aren't measurably affected. I'm pretty sure that the Radeon 9600XT is one of the cards that is affected by disabling fast writes but I'm not sure about a 9600 Pro. You should leave the AGP speed at 4X but you might try to see if it runs faster with fast writes enabled. You could use 3DMark as a benchmark to see if it matters. Slowing down to AGP 4X is enough to solve most peoples' problems so disabling fast writes usually isn't necessary. But since it has a negligible effect on performance on most cards people just disable fast writes because they have a reputation for causing problems.
ATI drivers have a built in AGP tester called SMARTGART which can automatically find the fastest reliable settings for your AGP port. So even though AGP 8X and fast writes are enabled in the BIOS you can still end up only running at AGP 4X and fast writes disabled. It may have worked in the past because SMARTGART had slowed down you AGP port without you're knowing it. It's supposed to do all the testing automatically but its tests are so short that it often misses transient problems. SMARTGART's tests don't catch all problems so they allow you to manually limit your AGP port properties.
