I really don't see how IBM releasing the Power6 has anything to do with making Apple's switch to Intel look bad. Unless there was plans for an extremely cut down consumer derivative, which I don't think there ever were, then they are in completely unrelated markets. Power6 doesn't compete with the Core 2 Duo, it doesn't compete with the Core 2 Quad, it doesn't compete with Xeon DPs, it doesn't even compete with Xeon MPs (that Apple doesn't even use). The Power6 competes with the Itanium which is a product segment that even Apple's widest server expansion dreams probably never want to touch.
Besides, Power6 is likely exactly the reason why Apple had to switch to Intel. Between Power6 and the in-order PPC chips IBM was designing for the XBox360 and PS3 (and no those console chips have very little application in a Mac), IBM was spending all their resources in other areas and ignoring Apple. If Apple had stuck with PPC, there wouldn't have been a consumer Power6 derivative until 2008/2009 assuming Apple's begging would have any effect. Even if a cut-down Power6 could best Intel's ever improving Nehalem and 32nm Gesher shrink, Apple's market would have stagmated so much in the intervening 3 years that they likely wouldn't have anyone to sell it to.
Besides, Power6 is likely exactly the reason why Apple had to switch to Intel. Between Power6 and the in-order PPC chips IBM was designing for the XBox360 and PS3 (and no those console chips have very little application in a Mac), IBM was spending all their resources in other areas and ignoring Apple. If Apple had stuck with PPC, there wouldn't have been a consumer Power6 derivative until 2008/2009 assuming Apple's begging would have any effect. Even if a cut-down Power6 could best Intel's ever improving Nehalem and 32nm Gesher shrink, Apple's market would have stagmated so much in the intervening 3 years that they likely wouldn't have anyone to sell it to.