Few games can use more than 4 cores, and only few filters in Photoshop are multi thread.
Aperture won't receive update anymore, so no multi thread / GPU acceleration in the future.
Surfing obviously can't saturate your i5.
From memory, only Batman and GTA V can use more than 4 cores on my machine so far. By considering you have the top speed most up to date i5. I don't think CPU will be your limiting factor in the next few years (especially comparing to the GPU power in your machine, which is much much more limiting in modern game).
So, it seems you won't miss anything by not choosing the i7. Unless most of the games are CPU intensive in the next few years and they are very well optimised for multi thread operation (the chance of this is almost zero). Or Adobe suddenly highly optimise Photoshop for multi core (this is possible, but it will only save you few seconds when applying a filter, no big deal).
The i7 is much more useful in video work / multi VM scenario, but it seems you have nothing to do in this area.