The Pentium is indeed a solid CPU, but! When we move closer to games which uses more than 2 cores, Both the i5 and i7 blows it out of the Water. You're completely right, that the PER CORE performance is really equal, and when playing games that doesn't operate with more than 2 cores, you will most likely get the same result as with an i5 or i7
Now.. the Thing is, we're living in 2015 and almost ALL AAA games will use and operate with more than 2 cores, and by then your "beast gpu" will be bottlenecked.. This Means the i5 or i7 is more "future proof" than the Pentium.
Sorry for my bad English, I'm from Denmark..