the HD2000 on the i5 2400 can handle casual gaming needs, basicly think of ipad games and maybe a bit more, anything heaver games it can't run decent enough. Here is the link of the review.http://www.tomshardware.com/reviews/sandy-bridge-core-i7-2600k-core-i5-2500k,2833-7.html
also OS? you didn't mention if you need it or not.
cost saving wise, you can go with a h67 board like intel BOXDH67BLB3. It will save you about $25. The difference between h67 and z68 are:
no overclocking, 2400 can't overclock anyway
no quick response, that a SSD related technology and the main difference,
and its an micro atx board which means less pci-e slot, you don't need that many unless you got lot of addon card.http://www.newegg.com/Product/Product.aspx?Item=N82E16813121506