I had an Extreme4, and while it worked fairly well, I ended up returning it because of coil whine and getting a P8Z77-V Pro. The Asus board is silent, which was the most important thing for me.
Now, having tried both, I'd say the Asus is a nicer board in other ways too (although it should be, at $60 more cost). It overclocks with offset A LOT better than the ASrock, which I could only get stable using manual v-core at 4.6GHz on my 2500K. This meant it ran hotter and consumed more power at idle.
The only thing I'm missing from the ASRock was the lightning fast boot time.