I think that if they did go to 4.0ghz with the current architecture they would find that a lot of the chips would get speed binned and therefore it wouldn't be a cost efficient line to run.
But its good news to hear that Intel are finally pulling their finger out - hopefully we can see some AMD killing processors from them soon.
If they manage that - and with Nvidia's SLI chipset, they'll be back in the runnings for serious gamers