Hmm time for some reading
Although AMD would have to get out some serious performance to beat the current i7's. The 920s can be clocked to 3.5 gHz almost without a problem sometimes even below their stock 1.18V. And the i7 has a scarily high memory bandwidth.
IF this 4 gHz on air cooling isn't too difficult though, AMD could be in for some serious intel bashing if their pricing is all right. One of their main advantages is the reuse of old motherboards, which lowers the upgrade price dramatically.