To enter the discussion on Engines. I ran some analyses on Max Speeds in km/h in the different sections in the qualifications for Shanghai and splitted those per constructor.
For the losers: Renault is failing to pick up pace since the last race. RB didn't come a lot closer and Toro Rosso lost quite some pace to Williams. Also McLaren can not get the Honda running well. Gap to Williams is increasing.
Big Winners are Sauber and Mercedes in terms of pure pace.
Ofcourse top speed isn't everything, but it is a clear reflection of engine power the teams are getting from the engines.
Reading the data myself I am surprised as quite some positive press was written on Renault improvements; this just didn't happen in terms of speed. Sauber did some amazing stuff compared to Malaysia. And Manor coming from nowhere seem to get their engine under control.
Table with Max Speeds / Constructor / Race in qualification.