This comes from xbdestroya, moderator at e-mpire PS3 forum, generally honest and knowledgeable guy who conducts interviews with PS3 developers:
"Yes, the Inquirer is trash, but the RSX, pending further news (because it's still subject to change mind you), has been downgraded.
I don't expect a big performance decline due to this myself, and I'm sure you'll hear many a dev back me up on that point. PS3 = Cell well before it equals RSX, and indeed, I have a pretty monster Cell interview coming up in the next 24 hours.
PS - Incidently, I don't think RSX was downgraded because Sony couldn't reach the speeds onsistently, I think it was downgraded because to get from 500MHz to 550MHz would have required a voltage bump that wasn't worth the added wattage and thermal constraints to the system."