Your hypothetical 4GHz 800MHz fsb, 1MBl2 is equalled by a 2MBl2, 1066MHz fsb P4 at what clock speed?
But the bigger question is, what then?
Is Intel going to again double the cache to make the next faster chip?
Remember, Intel's new "value add" upsell approach (since they won't be raising the clockspeed) has a much larger cost in terms of increased design-cycle time as they are adding/changing logic.
AMD, bringing a brand-new and superior (to its previous) process on line will actually be able to raise the clockspeed.
fpg