I don't think the comment from cmi86 about FX6300 being 80% the performance of 3570K, although not "wrong," would be an accurate way to describe cpu performance difference. Don't get me wrong, I love AMD and my choice to build lower end pc would be based around FX6300, and I always recommended FX6300.
I think you really need to consider the 1~4 core performance vs 5~6 core performance as your guideline. Will you be mostly gaming, or transcoding videos, or opening a bunch of apps at once?? Do you plan to overlclock or not? I personally think that for most people, faster 4 core performance is better, so recommend lower end quad core ivy bridge (if not overclocking).
But here is something to help you consider.
1. 3570K (compared to FX6300) generally 60% faster when using 1~4 cores, and about equal using 6 threads or more.
2. 3350P (about $40 cheaper than 3570K, can't OC) compared to FX6300 OC'd to 4.5 Ghz is about 15% faster when using 1~4 cores, and about 25% slower using 6 threads or more, but 3350P uses MUCH less power. So with OC, FX6300 has advantage, but without the OC, 3350P wins all the way. Also remember, if you want to OC, you would probably need at least $25 more for aftermarket heatsink (i.e. hyper212 series).
So the bottom line is that you have to consider the pros and cons, and pick the best one for YOU. Find the overall budget, and play around with the parts combination to find the sweet spot for you.