Performance difference between Intel Core i3, i5 and i7

It depends. If the inner loop of your program fits into the L1 cache of both CPUs and memory speeds are the same, you won't see much difference.

If the inner loop fits into the 6MB L2 cache, but does not fit into the L2 cache of the CPU with 6MB L3 cache, then the program will be faster on the older CPU with the larger L2 cache.

But in general, the inner loop part of a program is very small.

Intel Turbo Boost only boosts the speed if the processor is not fully utilized. Their site is pretty vague on details, but I remember seeing that it's designed for when one core is being maxed out while the other cores are sitting idle. If you're using multiple cores, the processor is drawing too much power, or the processor is too hot, then Intel Turbo Boost will turn off and the processor will return to it's normal maximum speed.

All cores will technically be running at the full speed, but you can't utilize all the cores at the same time while boosted or the processor will return to the normal maximum.

Intel® Turbo Boost Technology provides more performance when needed on 4th generation Intel® Core™ processor-based systems. Intel® Turbo Boost Technology 2.0 automatically allows processor cores to run faster than the base operating frequency if they’re operating below power, current, and temperature specification limits.

Any of the following can set the upper limit of Intel Turbo Boost Technology 2.0 on a given workload:

• Number of active cores
• Estimated current consumption
• Estimated power consumption
• Processor temperature