I'm activating my WC around GW8. Salah has until then to prove his worth in points-per-mill. Right now he's still better than the other expensive midfielders, though. 1,92 PPM vs 1.5 (Hazard), 0,8 (Sterling), 0,58 (Sanchez), 1.06 (Eriksen), 0.64 (Sané). Pogba has really started well PPM wise with 2.43, and Alli isn't performing to bad either (1.86). Right now I wouldn't touch Pogba at all, though. Mané is leading the pack by a lot, obviously, with 2,92, but we'll see how this stat looks in 5 gameweeks and a tougher schedule.
I realize this is a very small sample size, which is why I'm waiting until around GW8, when the fixture difficulty change drastically for a lot of teams.