We already know that an i5 does not cut it in BF4, an i7 min would be the recommended. While the 2500k overclocked is a great chip (mine is), it's being worn down by new games, advances in software, limiting it's life expectancy with new releases.
A PSU would be good idea if he is not sure of it's brand.
An i5 is fine.
http://www.tomshardware.com/reviews/battlefield-4-graphics-card-performance,3634-10.html
An OCed 2500k (4.2Ghz) performs about the same as a 3960x and is only slightly behind at stock.