I wouldn't trust any of those "Gaming PCs" on Amazon on eBay as they tend to design them to look like they have impressive specs when they don't. They also tend to use low quality parts for things like the motherboard and power supply as you generally won't look at them when buying it.
You would be much better to get something from a proper custom computer manufacturer like Overclockers UK, Scan, PCSpecialist.etc, the price difference won't be that huge either as those Amazon ones seem pretty overpriced for what they are. I would also tend to get an Intel Core i5 over an 8 core AMD FX as they perform better in almost all tasks.