Horses for courses. With a 50MHz/128MB IIci, or a 33MHz/14MB PB180, as examples, I find that 7.6.1 behaves very quickly and elegantly indeed. On a Colour Classic it limps, and that outcome doesn't need labouring. 040-processor Macs I usually push to 8.1, for the reasons above, and I have no PowerPC of any colour running less than 8.6, and mostly 9.1 or 9.2.2, including G4/500MHz Beiges.
This is all part-and-parcel of coaxing the most out of our Macs, although it must be tempered with reality (RAM and expansion bus, mostly). It's to Apple's credit that many of its machines can be pushed far beyond their release configurations because that possibility was implicit in their designs. That's not to say that upgrading was designed into them, but it certainly wasn't designed out of them, either
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