CPU is just an estimate of what the game actually need, 1.8 G is still good to try. I suspect that games actually don't care, that is on paper only to complete the listing,
Using a quad core to approximate the performance requirement might work, but it might not, or might just squeeze by with the 2 cores because of what I said as "not care". Extra cores need the support of modern programming to be leveraged, if the game is written to utilize a specific # of cores, that's it, it would not call for more cores. Nor will those extra cores be dumped back in as extra GHz to be used, that won't happen because that's not even what a CPU core is about.
Adding cores is the province of business machines. Just as an aside if you actually think about that. Typical consumer grade electronics do not support such action.