Well, the G3 is faster than the 604e, the G3's system bus is faster (66MHz with overclocking possible in a G3 versus 50MHz max in a 7600), the RAM is faster, plus the PCI slots are faster. But fast is not the same as up to expectation for all needs.
On the other side of the coin, my personal favourite beige PCI Mac is still the 8600, especially in its 604ev/300MHz variant.... It will take five (count 'em) hard drives in addition to the CD and floppy, and the power supply is much higher-end than the ones in the 7xxx or G3 series (the latter won't even power-off a monitor when you shut it down!). RAM is cheap and plentiful for it, and you get fully five (count 'em) more RAM slots than you get in a G3. There are also, as I have said elsewhere, good things to be said in favour of the 604e, especially with a (rare) 1MB L2 cache chip installed.