I know I would save for another CPU, but you did say that wasn't an option so here are a few things about the CPUs. I would say these are two of the biggest differences:
i7 - "More memory bandwidth, available to this processor, helps to eliminate memory bottlenecks. It results in increased performance in memory bound tasks."
i5- "The microprocessor comes with integrated HD 2000 Graphics Processing Unit. While this graphics is not fast enough to play latest games with all settings on, it can be used for casual gaming and 3D applications."
That said, while they are both older CPUs, the i7 is older and thus has an older socket type. Finding a motherboard you make it sound like might be easy, but again, being as old as it is, I would stick to something a little newer. If you're looking to game (or really anything), I think the i5 is just fine for now. If you're looking to try and upgrade at all, I would wait and continue to save so the gains you get are more substantial.
Some reading if you like graphs and charts...
http://www.cpu-world.com/Compare/373/Intel_Core_i5_i5-2300_vs_Intel_Core_i7_i7-960.html