Is this a good fast gaming PC?

Solution
I would be really wary of that power supply on the Lenovo, though. I'd change that out before changing out any other part, probably even before even using the machine. Otherwise, though, it seems like a rather solid deal if you prefer not to build.
If you have to go with either, I'd go with the Lenovo. The i5 will fare better in many games over the FX-6300, and both of them use a GTX 750 Ti for graphics. Plus, the Lenovo is cheaper.

Neither of these are particularly powerful, though. The 750 Ti is an entry level card. It will game well at medium-low settings at 1080p, but don't expect ultra settings all the time or anything like that.
 
No, it's a low end, entry level gaming machine that's WAY too expensive for what you're getting plus iBuypower and CyberPowerPC both are well known for poorly configured rigs that have have RMA rates. Basically, they suck. I'd never buy one of their units. For that price you could just about build a really decent i5 gaming machine. If you have doubts about your ability to do that, I'd consider buying a decent prebuilt and adding your own graphics card, which just about any ten year old could do, and would probably cost a lot less for a much better result.
 


The Lenovo machine seems surprisingly good, though. For $600, a build with an i5 and a 750 Ti is not bad, specially since it includes Windows. Then again, the quality of the other components could be crap, but it's not a terrible alternative.
 
Oh, wow, never mind; the Lenovo one comes with a 280W power supply. That is as sketchy as it gets. If you get that one, I'd replace that PSU as soon as possible. You can get a decent quality unit and still be under the cost of the other machine. At this point, though, we would get much better quality from building a machine instead.
 
I would be really wary of that power supply on the Lenovo, though. I'd change that out before changing out any other part, probably even before even using the machine. Otherwise, though, it seems like a rather solid deal if you prefer not to build.
 
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The 750 Ti is still a decent card. Sure, something like a 960 would be nicer, but we don't expect pre-builts to be that well-balanced 😛 I don't think it would be a huge issue, and it would be better to save up and get a newer card when next generation cards start appearing.
 
I would choose this http://www.officedepot.com/a/products/212292/EVGA-500W-80Plus-Power-Supply-Unit/?cm_mmc=PLA-_-Google-_-Computer_Parts_Upgrades-_-212292-VQ6-42102244556-VQ16c-VQ17-pla-VQ18-online-VQ19-212292-VQ20-18283950120-VQ21- power supply for 39 dollars and keep the 750ti graphics card