What will be your main use for this pc?
If it is for gaming, processor core speed is all important.
I5 and I3 both have 4 threads.
I3-6100 has a single thread passmark rating of 2102.
I5-4590 is similar at 2115.
I5-6500 is 1943.
I5-4460 is 1948
I5-6400 is 1825
Really, all are good gamers. Just see which one is priced best.