For someone like myself who's an average computer user who doesn't do graphics would I notice the difference in speed between a Windows 7 i3cpu computer and an i6 cpu computer?
There is no such thing as an i6 CPU, there are i3, i5 and i7.
If all you do is browse the net, store pictures, watch videos, listen to music, use office software, your average stuff, then an i3 would be plenty. I would actually say go for an AMD Athlon II x2 instead as it is cheaper, but would still give ample levels of performance