If it is not able to make the 100MHz bus (which brings the pci/agp back into 33/66mhz specs) then it is doubtful that you are going to make the 90mhz bus which takes the pci/agp back out of spec. In other words, for the pci/agp bus it is more likely to make the 100MHz system bus than 83. Conversely, if you were able to make the 83mhz then you would very likely make the 100. Since you can not make the 83, then you will not make the 90 as this also takes the pci/agp out of spec. Only 66/100/133 are pci/agp spec'd to 33/66. All others are following out of spec multiples.
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