Ill add in that getting the extra power under the hood now might make it possible for you to ust the rig longer. As things keep progressing you may end up getting a program in the future that would take full advantage of the i7.
This is true if you have money to spare at this point. The price difference between the 2500K and 2600K is about $100. The question the user will have to ask is whether they expect to see that much value down the road in whatever they are doing. Just keep in mind that whatever is the pip right now will be on sale for half the price next year.