If you're going for a non-overclocking build then take an i5 3570. The Z75 motherboard is fine.
The real difference is that the i5 3570K can be easily overclocked by 25-30% and will therefore last you far longer before you need to upgrade. Later down the road if you want to OC for a bump in system/application performance (good for games too) an i5 3570K will let you do it, an i5 3470 won't.
To sum it up:
- Additional $20 on CPU - 5 3570K - $219
- Additional $15 on a motherboard with higher quality VRM's/features - ASRock Z77 Pro3 - $95
- Additional $15-19 on an aftermarket cooler to allow a moderate OC and silence - CoolerMaster Hyper212+ or Xigmatek Gaia - $15-19
So that's a $45-50 increase to greatly "futureproof" your CPU/Mobo setup. OR you can spend that $50 on a slightly better GPU (660 ti / 7870 / 7950). Up to you.
Oh and you don't need a Seasonic X650, it's waaay overkill. Get this instead, it's more than enough:
SeaSonic G Series 550w - $69.99 ($54.99 after $15 rebate)
Bam, $35 saving.
And then you can scrape up a bit more money from somewhere to buy a 120GB SSD because no PC build is truly complete without an SSD >_<