In some newer games the FX-6100 beats the X6. It's not as clear cut as it used to be for FX vs. Phenom II
I would rather get an FX-6100 or an FX-8120 at this point. I am not seeing X6 holding on to the gaming performance in latest benchmarks.
Here is another way to think about your situation:
Let's say you get the FX-6100 for $122 or FX-8120 for $144. Core i5-3470 is
$185 after $15 off.
When you'll buy all the other parts, your desktop will probably cost you $600-700 or more, if you get a new monitor.
Suddenly the AMD system will be just $60-80 less but in the grand scheme of a $600-700 system.
Will Core i5-3470 be > 10% faster? In games it will be, especially minimum frames and in strategy, RPGs and MMOs if you play those. Over the next 3 years for example, you may want to upgrade the GPU 1 more time. Well that i5-3470 CPU will cope a lot better with games. Over 3 years, that extra $90-100 on an Intel desktop system will amount to just $30-35 a year. So ask yourself, is it worth saving $90-100 over the next 3 years you'll use this system to sacrifice CPU performance, especially if you plan to add a $300 gaming GPU? Imo, no.
Between the Phenom II and FX-6100, I'd just go for the FX-6100. At that point, you'll still have similar slow rigs but at least with Bulldozer, lower idle and load power consumption:
I was even thinking of putting together a budget AMD rig and I still can't justify only $60 CPU savings over a Core i5 over keeping it for 3-4 years. Also, I find that Intel CPUs have higher resale value so in the end the actual cost of ownership isn't that much if you upgrade often and sell off a 2 year old Intel platform for example.