Since you are not asking for a specific model number it is hard for us to make the comparison.
The following link is comparing an I7, I5 and I3 processor. All of them are Ivy Bridge processors.
- The I7 processor is usually faster than the other ones. It comes with 8MB of smart cache, Intel® Turbo Boost Technology and Intel® Hyper-Threading Technology.
- The I5 processor is usually faster than an I3 processor. It comes with 6MB of smart cache and Intel® Turbo Boost Technology. No Intel® Hyper-Threading Technology included.
- Finally, the I3 processors come with 3MB of smart cache and Intel® Hyper-Threading Technology. No Turbo Boost Technology.
Please check this thread with information about those technologies.
Here are some link you may want to check http://www.youtube.com/watch?v=JM31kX93fHU