I'm confused.....in 1st sentence you said you were using a Z68 MoBo....last you said H67. The latter has very limited overclocking options.
With the Z68 or P67, here's my recommendation:
$25 Hyper 212 - Good for 4.4 - 4.5 Ghz OC's
http://www.tweaktown.com/reviews/2904/cooler_master_hyper_212_plus_cpu_cooler/index6.html
$50 Scythe Mugen 3 or Hyper 612 PWM - Good for 4.6 - 4.7 GHz OC's (5-7C better than Hyper 212)
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=797&Itemid=62&limit=1&limitstart=4
$80 - Thermalright Silver Arrow - Good for 4.8 - 5.0GHz OC's (7-10C better than Hyper 212)
http://benchmarkreviews.com/index.php?option=com_content&task=view&id=674&Itemid=62
If I may suggest, the 2600k really isn't gonna rock ya socks off over the 2500k in gaming.....the 0.1 Ghz stock speed increase can easily be offset as ya have a bit more OC room overclocking wise due to the fact that the 2600k's hyperthreading really doesn't help in gaming and the extra 4 virtual cores can mean an extra 7C or more in CPU temps. When I build machine for someone, I create separate BIOS profiles (selectable at boot in the BIOS) which can be chosen at boot ..... Here's an example of my 1st day attempts at OC'ing a 2600k and the temps, voltages and LLC on the 4 cores:
Stock 51,53, 53, 51 (1.224) LLC = Auto
4.0 Ghz 52, 54, 55, 52 (1.016-1.024) LLC = Auto
4.2 GHz 54, 56, 57, 55 (1.256 - 1.264) LLC = Auto
4.4 Ghz 56, 60, 60, 67 (1.280 - 1.288) LLC = Auto
4.6 Ghz 62, 66, 68, 65 (1.360 - 1.368) LLC = High
4.8 Ghz 71, 77, 79, 72 (1.408 - 1.416) LLC = Ultra High*
Those were all w/ HT on and core temps dropped 7-10C on the cores when HT was disabled on the 4.8Ghz boot (left it on on other speeds). With TIM curing and tweaking I was able to drop those temps and voltages a bit.
With the $100 savings dropping down to the 2500k, you could grab two of these instead of the single 570
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121425
That would boost ya fps from performance from 525 fps to 862 fps based upon Guru3D's game test suite ..... a whopping 65% speed increase.
Here's a suggested build for $1414 with those two GFX cards
Case - $ 115 - Corsaie Carbide 500R
http://www.newegg.com/Product/Product.aspx?Item=N82E16811139010
PSU - $ 90 - XFX Core Edition-850
http://www.newegg.com/Product/Product.aspx?Item=N82E16817207011
MoBo - $ 210 - ASUS P8Z68-V PRO/GEN3
http://www.newegg.com/Product/Product.aspx?Item=N82E16813131790
CPU - $ 220 - Intel Core i7-2500K
http://www.newegg.com/Product/Product.aspx?Item=N82E16819115072
Cooler - $ 50 - CM Hyper 612 PWM
http://www.newegg.com/Product/Product.aspx?Item=N82E16835103103
RAM - $ 47 - (2 x 4GB) Corsair Vengeance
http://www.newegg.com/Product/Product.aspx?Item=N82E16820233186
GFX - $ 230 - Asus GTX 560 900Mhz
http://www.newegg.com/Product/Product.aspx?Item=N82E16814121425
GFX - $ 230 - Same
HD - $ 150 - Spinpoint F3 1TB
http://www.newegg.com/Product/Product.aspx?Item=N82E16822152185
SSD - Later - 120 GB Mushkin Chronos Deluxe
http://www.newegg.com/Product/Product.aspx?Item=N82E16820226225
DVD Writer - $ 22 - Asus 24X DRW-24B3L w/ LS
http://www.newegg.com/Product/Product.aspx?Item=N82E16827135221
Card Reader $ 50 AeroCool FP-01 55
http://www.newegg.com/Product/Product.aspx?Item=N82E16820314001
You should be able to OC the GFX cards a bit further .... I usually go to around 1000 but have seen them done to 1070 MHz ....
http://www.pureoverclock.com/review.php?id=1201&page=17