5th gen i3 vs 4th gen i5

Warukyure

Estimable
4th Gen i5 is better than a 5th Gen i3. CPUs don't REALLY get obsolete that fast. There are a few things that i5's will always be much better at doing such as hyper threading and turbo boost.

Also Intel's focus lately is to make a CPU that lasts longer on battery life, so there isn't too much for improvements.

Lastly, generalized, 5th gen CPUs are pretty much die shrink, 6th Gen is where the improvements would be.
 

The desktop i5 is clearly a better buy.
The i5 has 4 physical cores, no hyperthreading, and turbo boost.
The i3 has 2 physical cores, hyperthreading, and turbo boost.

Without question the i5 is better. On top of that Broadwell (5th gen) is just a die shrink of Haswell (4th gen). So unless you're going to use the integrated GPU extensively, there is virtually no performance difference between the two generations. Broadwell just has lower power consumption, which you don't really care about on a desktop.

On laptops it's not so clear.
The i5 has 2 physical cores, hyperthreading, and turbo boost.
The i3 has 2 physical cores, hyperthreading, and no turbo boost.

Prior to Haswell, the turbo boost on most of the i5 line was pretty modest - about 5%-15% base clock speed. Not really worth the extra $50-$100 vendors were charging, and the i3 was a better value (the fact that Apple doesn't offer an i3 laptop was a big tip-off where the fat profit margins were). Only the ULV processors got bigger turbo boosts which made the i5 worthwhile.

Beginning with Haswell, the main i5 line became ULV processors (end in a U or Y), so most i5 laptops started to get turbo boosts of 30%-65%. So suddenly the i5 became a good buy compared to an i3 with the same base clock speed.

OTOH, Broadwell introduces some impressive battery life savings, and you're more likely to end up using the integrated GPU on a laptop.

So the answer becomes: If CPU performance is what's most important to you, then get the 4th gen i5. If battery life and integrated graphics performance is most important to you, get the 5th gen i3.