Currently the only details I can find about the microarchitecture is either press waffle or things reverse engineered via timing (you can look for bumps in graphs to find the widths of various speculative features of the CPU).

It would be very Apple not to publish any (Fucking sad if true)

Edit: Intel, like them or not, have genuinely very good documentation (Much better than AMD's) and seem to have really thought about actually using their performance - AMD can really deliver the goods on their terms, but they still lag behind in both software (particular compared to Nvidia) and documentation (Intel's optimization manual is 850 pages; AMD's is 45 pages). AMD basically give you a raw list of RDPMC event assignments to play with, Intel actually tell you how to use them.