If we are talking defensive contributions:
Benat (per game): 2.1 tackles, 1.1 interceptions
Barry (per game): 2 tackles, 1.6 interceptions
Song (per game): 2 tackles, 2.1 interceptions
Not a lot between them really and none of them hugely impressive. Benat is the most creative of the three though (7 assists this season).
I love watching Benat would be a really good 'option' if we were to completely remake our midfield (with Garcia and Barry leaving), but not sure about him as Yaya's partner. Ideally we need someone who will be all over the place next to Yaya, making tackles and pressing opponents... and ideally someone who can do MORE than just tackle and play simple passes (this was a criticism at De Jong and is one at Garcia).
Some other central midfield defensive stats for perspective/comparisons.
Vidal: 5.1 tackles, 1.4 interceptions
Lucas Leiva: 4.6 tackles, 2.5 interceptions
Lars Bender: 4.3 tackles, 2.7 interceptions
Ramires: 3.4 tackles, 1.6 interceptions
Sandro: 3.3 tackles, 3.6 interceptions
Matuidi: 3.3 tackles, 3.6 interceptions
Arteta: 3.3 tackles, 2.8 interceptions
Alonso: 3.3 tackles, 2 interceptions
Busquets: 2.9 tackles, 1.6 interceptions
Pirlo: 2.7 tackles, 1.4 interceptions
Luis Gustavo: 2.6 tackles, 1.6 interceptions
Gundogan: 2.4 tackles, 2.3 interceptions
Carrick: 2.4 tackles, 2.2 interceptions
De Jong: 2.4 tackles, 1.3 interceptions
Inler: 2.4 tackles, 1.1 interceptions
Yaya: 1.2 tackles, 0.9 interceptions (and why he is NOT a "defensive midfielder")
Javi Garcia: 1.1 tackles, 1.2 interceptions