I don't consider dual cores to be old and ready for the scrap heap {...]
Gaming machines and number crunchers aside ...
Dual cores run just fine. Really, I think it's more of a matter of processor speed than anything. Buy the top-of-the-line model (fastest CPU), new or used, 2-8 cores, and they're all gonna fly.
I had a friend that worked at the Intel Chandler Campus (fab). He's in jail now for stealing CPUs off the production lines. The idiot took whole trays dumped them in the trash, came back at night, recovered them from the dumpster and sold them on the black market. LoL !

He told me the CPUs all came off the same line. Some of the CPUs ran faster than the others, even though they were made in the same batch. That is, some CPUs tested out faster than others, so they would simply mark them accordingly. Some ran shittier than others, for lack of a different term, and they were marked with a lower speed.
Anyway my dual core laptop was the fastest machine in the house, until I bought the i5 desktop and i7 lappy. To tell you the truth, there isn't an ounce of difference, in performance, between the lot. They all scream !
Single core ... meh ! They're all past their prime, IMO.
