Overall in the real world,the GTX 570 is a more powerful card (however uses more power). The pre built is not exactly fantastic, running on an outdated AMD processor and a sub-par motherboard. The PSU brand is unheard of and would probably break the system in a few days, and the case isn't exactly beautiful.
Your build however is very well conceptualised and thought out, with quality and new parts.
Overall, your build would outperform the pre-built easily, however I recommend a single change. The GTX 570, whilst powerful, is an older generation card, and you could probably pick up an AMD 7850 for around the same price. They perform fairly equally, however the 7850 will overclock in a much easier fashion, and require less power overall (cut down on those bills lol).
Anyway, I wish you luck, but please don't buy the pre-built haha!