I wouldn't bother with a PowerPC upgrade. They're exceedingly rare, and take up the space where a PDS card would go, (don't know about you, but I can't live without my Ethernet), and to be honest I'd rather have a fast 68k than a slow PowerPC. (while I believe there were faster 3rd party upgrades, the Apple one was a 50 Mhz 601, from memory)

I have an LC475 (same machine just in a different case), which is nicely souped up. Mine has a full '040, max VRAM (a must have - the max 1MB VRAM will give you 16 bit colour at up to 832x624, or 8 bit colour at up to 1152x870, whereas the standard 512k will only give you 8 bit at up to 832x624, and 4 bit at up to 1152x870) 68MB of RAM (64MB SIMM, and yes, 128MB SIMMs do work, just be warned that with 64+ MB of RAM the startup RAM test will take ages), 2GB HDD, and ethernet. With all this, triple booting 7.1, 7.6.1 and 8.1, its a nice, fast little box.