Generally speaking, assuming same # of cores and same clockspeed....
1st generation Core i3/i5/i7 CPUs are on average almost 12% more powerful than C2D / C2Q CPUs.
Sandy Bridge (2nd gen) Core i3/i5/i7 are on average 12% more powerful than the 1st gen CPUs.
Ivy Bridge (3rd gen) Core i3/i5/i7 are on average 6% more powerful than Sandy Bridge CPUs.
If you know how to multiply, then you can calculate the rough performance increase.