For the games I play I feel like it would be a lot of wasted cash to move up to a good i5.
The last "upgrade" I did was from an athlon ii x2 to a phenom ii x3 and I have yet to notice a game where the change makes any real difference.
This is probably because I'm just not playing the "right" games. I don't play mmos, nor fps shooters like battlefield. Most of my time is spent playing older titles.
Some of the more recent games I played (dishonored, deus ex human rev, thief, mirror's edge) haven't required much of a cpu.
I mainly just want to max out Skyrim with quite a few graphics mods.
I know for a fact the pentium will provide far better single core performance than what I have now, especially when overclocked. Even a game using three cores properly would probably run fast on the pentium than it would on the phenom triple core I have at this time.
Some games I do find are cpu limited when I want to run at 60 fps but they are only maxing out 2 cores (recent assassin's creed games for example).