Yeah, usually you see 8.0 or 8.1 on the fast 68k's and ANY PPC, 7.5.x on the mid-68k's, and anything lower on the lower-end 68k's, version depending on the amount of RAM. I can only imagine that a PPC under an early version of System 7 would boot "wicked fast".
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PPC Macs:

• Power Macintosh G4
  
• B&W Power Macintosh G4
  
• Power Macintosh 6500/225