Better motherboard? well generally the more features that you want, the better it is for you
you can spend $20 or $200 on a motherboard, the performance will be exactly the same.
the Extreme 4 is a good choise and it's on the latest Z77, so why not?
You know just having an i5 3570k wont give you good gaming performance... at all
you need a graphics card, I don't mean to insult your intelligence but I see some people spending $X,XXX on a "gaming" computer and think an i7 is all you need and don't even bother with a graphics card XD
No thats great thanks! Was not insulted I had in my head to start off getting a good base of a computer reasonably priced but has some oomph with the ability to keep upgrading the graphics card as I needed however just had not researched that one yet
ASRock Z77 Pro3 is really well priced as well at the moment, USB, loads of slots, nice cooler PCB, Z77, loads of fan headers, good I/O, supports SLi/Crossfire, all that good shet.
3570k is good aswell like you mentioned but if you're just going for like a 7850 like mentioned above, get an i3 3220, half the price of the 3570k and same gaming performance until you get up to like a 7950/GTX 670 (you can always swap out the CPU easily at a later date)