The onboard video chip will suffice for your prescribed scenario. K series CPU's have a better video processor. Its advantages are debatable but considering the price difference is not huge, i'll recommend you to get the i5 2500k.
A discrete GPU is better than a integrated period, it does not hug system resources (ram) like IGP's do. But overall a I5 2500K on a Z68 board is a better combination than a I5 2500 on a H67 board especially if you can use quick sync.