Not that way anymore really. With i3s being so cheap, they are 100% the way to go. Better than the fx6300 even in most games.
I would get an i3 for sure.
GHZ cannot be compared between two different CPUs. For example a 5ghz Athlon 760k will lose every time to a 3.5ghz i5. It is about architecture, not speed. Speed only matters when comparing two identical CPUs.