The 2.8ghz imac that I own is a 3.0ghz downclocked to 2.8ghz. when I had it apart the chip itself says 3.0ghz on the heat sink. My hd2600 gpu is also under clocked from an xt to a pro. And so are last years macbook pros. Maybe you should google this for more info. There are numerous reports of under clocked chips coming from macbooks and imacs. If I felt like tearing my imac apart again I would send you a pic of my 2.8extreme that is actually a 3.0 chip. I cant speak for the quad core products because i don't have one. but all of my macs are under clocked. 2007 imac, 2008 macbook pro, late 2008 macbook have all been apart at some point or another and all had higher clock speed on the chip than what os x and apple says.
my A4 info was based on engagets article stating that it was an A9 mp chip. which is also stated in articles from wired.com and macworld.com. The only thing I can find about it being an A8 is wiki and is from jan 2010.
"A4 is a System-on-a-Chip, or SOC, that integrates the main processor [ARM Cortex-A9 MPCore i.e. Multi-Processing Core, identical to ones used in nVidia Tegra and Qualcomm Snapdragon] with graphics silicon [ARM Mali 50-Series GPU], and other functions like the memory controller on one piece of silicon not unlike what Intel is trying to achieve with its future Moorestown Atom processor that debuted inside LGs Smartphone". This quote is from Cult of mac interview with member of apple ipad design team. The A8 chip is in the iphone 3gs running at 600mhz and apple claims that the ipad and iphone 4 have a completely NEW chip in them, not old chip with a faster clock speed. According to the specs on ARM's website for the A9 chip it clocks at 1.3ghz but the ARM system that is in the A4 is clocked at 1ghz. The A4 specs on wired.com from May 21st says:
ARM Cortex A9-based architecture, modified by Apple
mulricore
1 Ghz main frequency
2 MB L2 Cache
45 nanometer process
300 milliwatt max power use
ARM NEON Processing Media Engine
And apple acquired PA semi not ARM which was my mistake. But ARM designed both A8 and A9 chips.
sorry for the one false statement about ARM being purchased by apple. PA semi was purchased by apple in 2008.
Might want to look at this article:
http://www.eetimes.com/showArticle.jhtml?articleID=225700447&cid=NL_eet