As mentioned before
has a G3 Cache Utility that "works on the Apple Power
G3-233 (and possibly the G3-266) backside cache." A reader reports that it also adjusts the cache speed on the PowerBook G3. He writes: "The PowerBook G3 backside cache runs at 100MHz, which is a 2.5:1 ratio compared to the CPU speed of 250MHz. MacBench 4.0 gave a CPU score of 751 to my PowerBook G3 at the stock cache speed. And after setting the cache to 125MHz, or 2:1, MacBench reported a CPU score of 798."