I did some brief checking based on the Spanish GP, and even though Button was having issues at the time, he was still faster last year than he was this year, by around 6/10ths. Also, the pole time (Lewis') was a second slower than this seasons, which indicates that relatively, McLaren have lost 1.6 seconds, with last years car it would only be 1 second off the pace, notwithstanding any developments that could have been made.