Barefeats was G5 tests, not G4 tests, which seem to have disappeared. But they're all useless. They're comparing the G4 a couple of generations ago against the fastest from Intel and AMD at the time. The technology difference for the PPC from those tests to what would be used in this system could be compared to the difference between the Athlon XP's Palomino and Barton cores, or maybe even between a Thunderbird and Barton, depending on what Apple pulls.
Aside from that, we need to find a G4 1.25 vs. the latest Celeron or Sempron. That's the price range we're talking about here.
Because it doesn't really matter what we think - what matters is what we can prove. So I'm challenging you to a duel.