What is the performance difference between the standard size ATX motherboard and a mATX? I know the size is smaller but other than that I don't know much else. Is a mATX motherboard good enough to build a gaming PC or should I stick with a full size ATX?
If they have the same chipset it will be exactly same performance. AMD partners do not make any AM3+ mATX boards with the better chipsets but Intel partners do. So it really depends on what direction you are going.