I don't know about the 40" deck but I went to 4 different dealers and they all told me the same and that was to buy the Grandstand 36" They all told me I would see any reduction in productivity between the two and it was a better machine than the 40".
The 40"and 36" run the same motor and the nice thing about the 36" is you don't have any issues with gated yards. I can tell you I've been super happy with the 36" and I've put 180hrs on it since August.
G & G Lawn Care
2015 F 150 XLT 4x2 Super Crew