Oddly enough, a 5GHz dual core proc doesn't exist, nor does a 5GHz normal proc.
Unless you had a massive cooling system, it's doubtful you can even overclock the latest dual core proc to those speeds.
A 5GHz dual core would mean 2 x 5GHz procs... does not exist.
I think your friend either doesn't know what he's talking about, or just has a 2.5GHz dual core proc, which does exist.
As as REV0LUTI0NIZED said, just because you have a 'powerful' PC, doesn't mean you know anything.