They've traded clock speed for complexity, Cell should clock up to 4GHz without problems (it's held lower in the PS3 because they don't want it becoming too noisy).
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Cell is not the only processor design to aim for +3Ghz. Design is one thing while resulting yields in mass production is another.
If one notices, AMD’s process yield (week 16, 2005)A64 FX55(San Diego)@3.1Ghz*(via overclcoking) air cooled is very close to Cell’s 3.2Ghz end-user delivery. Similar week 16 fabrication, A64 X2 4800+has been over clocked to 2.8Ghz*.
*Successfully runs Windows and usual benchmarking suits.
Liquid cooling enables week 16 2005 A64s to run as high as 3.4Ghz*. Similar week 16 2005 yields, has been pushed beyond 4Ghz (only boots the BIOS screen). A64 over clocking has proven that OOO designs can be pushed toward 4Ghz. PIV already past 4Ghz via it’s double pump units (PS; Pentium M doesn’t have these designs).
At 4GHz the PPE alone should kick a 2.7GHz 970's ass.
Invalid comparison since you did not compare the same processor design at Q1 2006 yields. 2.7Ghz 970FX is available today while PS3/Cell is currently MIA.
One has to remember that Cell's PPE is an in-order, two-issue superscalar Power core design.
