first of all,there are those who say that at this moment there is no real need for a quad core as far as general computing is concerned,,if on the other hand you are engaged in the kind of usage that requires multi cores video editing ,for example...
dual cores,,take for example the AMD 5000be,it's native ghz is 2.4 and can easily go higher,then there is the AMD 6400be @3.2ghz which except for the 1m onboard cache,is the same as the 5000be,and costs almost 2x the 5000be..
so what it boils down to is what you are going to do with your system,how much you want to spend,how long your selections will last,,and what kind of upgrade path will your selections offer you as time goes by..
and as for playing crysis on high with no lag,well that is your choice,methinks that there are better games out and coming in terms of storyline and player involvement,,although if you can run crysis at high settings with no problems........