Laps 32 to 39. Button caught up to Nasr at 40 and got stuck behind him.
http://en.mclarenf-1.com/index.php?page=chart&gp=956&graf=3&dr1=Jenson Button&dr2=Nico Rosberg
Now let's take Force India
Perez,
http://en.mclarenf-1.com/index.php?page=chart&gp=956&graf=3&dr1=Jenson Button&dr2=Sergio Perez
Yes Button fitted new mediums later than Perez but over the course of the race Button was MUCH faster than Perez. Look at the time when Button was running in clean air.
Hulk,
http://en.mclarenf-1.com/index.php?page=chart&gp=956&graf=3&dr1=Jenson Button&dr2=Nico Hulkenberg
They were more or less neck and neck with Button having superior medium tyre pace.
[analysis of other teams]
So yeah they have made a HUGE step and i believe this will be the slowest race pace they will have all year and they will improve more than almost everyone else.
They are faster than FI,Haas,Sauber,Manor,Renault and almost neck and neck with STR. They were faster than one of the Williams (a merc powered) car.
Yes i think the engine still lacks a grunt but they are ahead of Renault right now in peak power but not how the power is delivered. With McLaren's and Honda's $$$$ i believe they will outpace the development rate of FI,STR and Williams and 4th Fastest car is easily doable. RBR is still a tall task but seeing the race pace of Jenson , we can be optimistic. ALonso will be a bit faster than him.
TLDR : McLaren is faster than most of you think it is.