Increased Bus Speed --> Decreased CPUMark Performance. How come?

[Orpheuss]

I just upgraded my TX97-Board with K6-2 400 o/c 500 using 2.4V. The system runs stable at 52C. Gonna add a better heatsink soon.
I run Winbench97 to compare results from the original 400Mhz setting (6x66), 450Mhz (6x75) and 500Mhz (6x83).
The results showed increased performance in all tests, corresponding to the increased bus speed.
The only strange result is the CPUMark16 and CPUMark32. For these two, the results goes the opposite.
CPUMark16 results for 400,450 & 500 are: 580, 547, 518 and
CPUMark32 results for 400, 450 & 500 are: 594, 509, Unable to complete

Why is it decreasing, instead of increasing? What is the logic behind this?
With SisopSandra99, the results of CPU and Multimedia tests are very consistent to the increased bandwidth.

Anybody can help me explain how this happens?
Thanks.

[diablovision]

Why are you running 400 as 6x66? 4x100 would give you much better performance. Go for 4.5x100 and 5.0x100...

[Orpheuss]

Because basically TX97 board is a Socket-7 board and does not support 100-MHz FSB. The max. is 83Mhz. That is why I overclk my processor using 6x83.