The G3 Sonnet is confusing me. It says the bus speed is 250 (should be 500?), but I read that it's 2:1. I don't know what 2:1 means but 250 times 2 is 500. Also, in the system profiler it tells me that there's 512k of L2 cache but there's actually 1M on that card. The Sonnet program called Metronome says it has 1M though. Maybe this has two separate L2 caches of 512k, each at 250mhz a piece or something? That's my guess.
I don't know much about CPUs and how they work, but this G3 upgrade is blistering fast compared to the stock 233mhz. It's more than double speed it seems. The 233mhz doesn't even have inline or backside cache I don't think, just regular L1 and L2. Browsing through directories is much quicker now, and so is installing software, and there's generally less lag and hiccups.
OS8.6 also helps since the system requirements are a bit less, and plus there are less extensions.