OK, let's have a look at 3DMark to get some baseline data....
3DMark Sky Diver
We can glean quite a bit of information from the graph above. First of all, overclocking the Pentium predictably does nothing for the graphics score, as it's entirely GPU-bound. But we do see a 21% increase in the Physics score, interestingly not quite matching the 31% overclock we ran on our Pentium. It seems that Sky Diver's Physics test doesn't scale quite as linearly with clock speed as other CPU tests. At the same time, it doesn't appear to care much for the Core i3's Hyperthreading either, as the overclocked Pentium nearly matches the Core i3 in that regard. Probably the most important data point above is the difference in the Graphics Score between the Pentium and the Core i3; the latter is 30% ahead, which likely sets the maximum delta we'd see in any gaming scenario.
The Core i3-6100 is truly in another league all together. Its graphics score is 70% faster than the 4170's when using standard DDR4 RAM, and 79% faster when using fast RAM. And despite an identical clock speed, it scores 25% higher in the Physics test (29% higher with fast RAM). That's a huge win for a chip that drops into the same price class as the 4170, while actually using less power. We should note tha this delta might be a bit unrealistic, as there was one entire portion of the test that both the Pentium and Core i3-4170 could not complete, giving it a zero score.
3DMark Fire Strike
We decided to test Fire Strike to get a bit more information about our CPU's processing power, and for this test we dropped the stock-clocked Pentium to spare it a bit of embarrassment. Focus on the Physics data above - clearly these chips can't handle Fire Strike's graphics in any meaningful way. In this Physics test, which we've previously found to scale perfectly with both CPU clockspeed and CPU cores, and at about 50% with Hyperthreaded virtual cores, the Core i3-4170 has a commanding lead on the overclocked Pentium. Its 42% lead despite a 500MHz clock speed deficit indicates the potential of Hyperthreading when an application is designed to make use of it. But even the 4170 is beaten badly by the Core i3-6100, which is 17% ahead even when using standard DDR4-2133 memory. We'd guess that this is a better representation of the 6100's overall clock-for-clock lead on the 4170 than the bigger delta found in the Sky Diver benchmark.
Oh, yes, and for what it's worth, the 6100 is 60% ahead of the 4170 in the Graphics score using 2133MHz memory, and 66% ahead with fast 3000MHz memory. Unfortunately, the benchmark still ran like a slideshow, so you won't be wowing any of your friends showing this one off on your shiny new Core i3-6100!
Tomb Raider (2013)
Well, it seems that what we learned using 3DMark applies here as well. This game is completely GPU-bound on these processors, so much so that even a huge 30% overclock on our Pentium doesn't move framerates one bit. The Core i3-4170 fares just a bit better, with an average framerate 20% higher, but still very much in barely-playable territory. While we don't think this game would look very good at 720p, dropping to that resolution would certainly make the Core i3 playable, if not the Pentium as well.
Of course, the Core i3-6100 opens up whole new possibilities versus its predecessors. At 71% faster than the Core i3-4170 in this GPU-bound benchmark, we're starting to see the extent to which Intel has conjured up some serious magic with its newest Skylake line of built-in graphics processors. And running fast memory gives the chips another 7% boost.