If you don't mind waiting, you're not going to see massive gains by buying the more expensive system. If your concern is video playback, then you'll have to make sure you have graphics card that is appropriate for your system. The i5-750 is a solid processor that should suit your needs.
Alternatively, if you're also buying a new motherboard, then consider the AMD Phenom II X6 1055T and an appropriate motherboard. It will be a great processor for the type of work your computer will be doing. This could potentially end up being cheaper than an i5-750 build and perhaps even perform better for your usage.