we haven't even breached 5GHz out of more than 1% of current chips (and of those who do claim to have a stable 5GHz rig, most are running dangerously high volts for 24/7 use) and you're asking not just about 6GHz, but air cooled 6GHz
considering Intel capped the multiplier at 63 I highly doubt it, just because some SB chips are able to hit 5GHz doesn't mean we're suddenly going to leap forward another GHz, those really are the rare exception, just like there are an exceptional few 45nm chips that could do 4.4-4.5GHz
when we look at each process node, the realistic upper ends for stable computing on reasonable air cooling for quad cores have been:
65nm = 3.2-3.4GHz
45nm = 3.8-4.0GHz
32nm = 4.5-4.7GHz
I think we'll be lucky to see more than a 700MHz jump from SB's current practical range, so anywhere from 5.0 to 5.4GHz is where I'd predict practical air cooling will limit a majority of IvyBridge CPUs. Golden chips and/or high end cooling would likely net much faster clocks likely into the 5.5GHz range, but I think it will still be a pipe dream to expect 6GHz outside of supercooling and redonkulous volts
And if we really consider things like the fact that SandyBridge wasn't Intel's first foray into 32nm (they had a year to brush up on it with Westmere) and that Ivy will pop Intel's 22nm cherry, I think we should really be hoping IvyBridge gives us at least an easy 5GHz to at least break that milestone more than anything, it wouldn't be outside the realm of possibility for there to be a flaw somewhere along the line that severely limits Ivy's clocking potential beyond that of SandyBridge.
but yeah, i'd be surprised if we hit 6GHz on common air even by Haswell and believe it to be more likely that it will take Broadwell or Skylake to achieve 6GHz as a common milestone
of course I could be totally wrong, I'm just basing my guesses off of what we've seen from the past. Its always possible a new architecture throws us for a loop (although I doubt we see anything as drastic as Netburst from Haswell or Skylake) but that would only bring us to another point - would 6GHz even matter if its IPC isn't as fast as we're accustomed to? Right now another ~10% in IPC + a "guaranteed" 5GHz out of IB would be a solid upgrade from what SB "guarantees" us. Personally, I think 5.5GHz would be amazing, although I'm expecting something more along the lines of 5.2-5.3GHz (which would put it right in line with being 1GHz slower than its multiplier cap, much like how a realistic high end for Sandy is 4.7GHz, 1GHz slower than its 5.7GHz multi cap). But yeah, if IB can give us 6GHz on air I'd probably die from an epileptic nerdgasm.
^ nice summary and overview :thumbsup: