Are you sure it says 85/9500 and not 86/9600? The 200 MP card was only shipped in a 9600; the fastest DP card for the 9500 was 180MHz.
Anyway, the main difference between the x500 and x600 models is that the x600 models didn't have a L2 cache soldered to the logic board. The x500's L2 cache was slower than the CPU required, and apparently the machine couldn't (or wouldn't) disable or work around it. This kept the high-performance (200MP/250/300/350MHz) cards, which had their caches mounted directly on the CPU card, from running in those machines. Plus, some of those cards required more power than the standard power supply shipped in an x500 series could provide.
Anyway, the main difference between the x500 and x600 models is that the x600 models didn't have a L2 cache soldered to the logic board. The x500's L2 cache was slower than the CPU required, and apparently the machine couldn't (or wouldn't) disable or work around it. This kept the high-performance (200MP/250/300/350MHz) cards, which had their caches mounted directly on the CPU card, from running in those machines. Plus, some of those cards required more power than the standard power supply shipped in an x500 series could provide.