pur benchmarks dont say anything really , if you run apps on a PPC Mac that had been made to run on them they will perform today as good as they performed 5 years ago and even 5 years ago there had not been many apps on the market that could make any use really of dual core processors, even worth the new intel iMacs have trouble with old PPC apps,even apples own like final cut (yes of course you can upgrade for lots of money ), try to run office 2004 a simple program that even my iMac g3 can handle and you will find that even a modern i7 iMac wont be able to handle it even with rosetta ,you cant even run OS9 games proper , sheepshaver is just a bad compromise ,classic was far superior
Well under rosetta on my Mac Pro I can load all my PPC applications except SoundTrack Pro 1 just fine (It broke with 10.6.4) They also work fine on my White macBook (2.1 C2D) - so maybe it just depends on the application.