There's no benefits to the Z68 for you, the iGPU would be worthless unless you plan on creating MPEG-2/4 videos, and it would be a terrible waste of a OCZ Vertex 2 120GB SSD for SSD caching. SSD caching is meant as it sounds, using a small SSD 20-40GB + HDD where the frequently accessed data get copied to the SSD as a 'cache' similar to the HHD {Hybrid Hard Drives}. In your case install the OS + Apps on your SSD and Data on the HDD, it's twice as fast or more.
As far as a CPU, if you primarily 'Game' then the i5-2500K is the SAME as the i7-2600K {clock per clock} in Gaming; no difference. The Difference is for Applications that take advantage of the Hyper-Threading e.g. Adobe products, CAD, and Rendering Apps -- Games do not use Hyper-Threading. Example on my i7 980X gaming rig I turn HT off so my CPU, OC 4.6-5GHz, runs considerably cooler.
Tip:
SSD {OS + Apps} and HDD {Data} - you can easily change the defaults of Documents, Photos, Music, Downloads, etc -> http://hubpages.com/hub/Windows-7_-_Moving_My_Documents BTW always create a folder first and never make the 'D:' drive the location *always use a Folder*; in 'D:' create Documents, Photos, Music, Downloads folders before changing the default location.
Good Luck!
edit: fixed a typo