Well just look for any benchmarks comparing the two.It shouldn't bee too hard.Ill just give you a few examples.
http://www.tweaktown.com/reviews/4350/amd_fx_8150_bulldozer_gaming_performance_analysis/
http://www.guru3d.com/articles_pages/radeon_hd_7970_cpu_scaling_performance_review,1.html
http://www.techspot.com/review/452-amd-bulldozer-fx-cpus/page10.html
I tried to avoid most of the unreal gaming scenerios some reviewers do.Like playing with Tri-SLI or playing at 1024x768.
Generally the reason Intel's Core i5 processors are better for gaming is because they can do more instructions per cycle (clock).Basicly what that means is that Intel's CPU's are far superior to AMD's at the same clock speed with the same amount of cores.
And since AMD and Intel processors are clocked at similar frequencies, intel CPU's tend to have better single core performance.BUT since AMD's CPU's usually have twice more cores than their Intel competitors they usualy win in multicore applications.The thing is however that most games nowadays can take advantage of up to four cores.So basicly if you've got a 8 core AMD processor, half the cores aren't doing anything and the other half are working as hard as they can but they just can't perform anywhere near a Intel Core i5.
And now on to the cache.More cache doesn't help that much.Take for example the AMD Phenom II and the AMD Athlon II.The Phenom II has got 2MB L2 cache and 6MB L3 while the Athlon II has got only 2MB L2 cache.The difference is between 0 and 15 percent.That isn't too much really.
But Bulldozer is a totaly different thing.It's cache is SLOW and by slow i mean really really slow.It's latency is, if i remember correctly 50% higher than Intel's Sandy/Ivy bridge processors.
And lastly one of the reasons AMD's FX Series are so slow per core is because their cores share recources.They arent "full" cores.This basicly reduces their performance by around 20%.
And lastly Intel isnt awlays better than AMD for gaming.Intel's quad cores are better than every CPU AMD has to offer but everything below that is questionable.If the game you're playing can use four cores effectively, then a Phenom II X4 becomes a much better choice than a Core i3 and the same can be said for a FX 4170.Basicly if you're buying a gaming processor either buy a Core i5/i7 or an AMD.Intel's Core i3 and Pentium line of processors offer very poor multithreaded performance compared to competing AMD CPU's.