Like with the new Core i3 4th gen models, Core i5 models and Core i7 models. How much of a difference is there really between the Core i3-4130 and the Core i3-4340 or the i5-4430 and the i5-4670.
quite a big gap going from the i3 to the i5 because you are going from dual core to quad (on desktop cpus, but some laptop i5/i7 are dual also), but not as much to the i7, as that is still quad (except the super high end socket 2011 cpus).
The difference between the two i3s you listed would be pretty small, same for the two I5s. As Rob said the difference between an I3 and I5 is pretty dramatic. I5 to I7 is less of a difference.