> I saw one G4 PowerMac on eBay (not .de) that was advertised as an upgraded to
> 2.1GHz G4 CPU (single I think) a few days ago. I don't know if the auction has
> ended so I may not be able to find it again. I think it was the QuickSilver model.

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=220515258651

But that's a strange one:
- no mention of exact upgrade type (AFAIK 2.1 GHz didn't exist for any PowerMac G4 model)
- bus speed of 167 MHz and RAM speed of 333 MHz would indicate FW800/MDD model, for which the fastest upgrade I know of would be (dual) 1.8 GHz
- "Processor Manufacturer: IBM"