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
Mowers: Toro GS 36" Toro TurfMaster Cub Cadet Z-Force 48" Cub Cadet 98H & 999ES
Blowers:Stihl BR 550 Stihl BR 380 Stihl BR 200Trimmers: Stihl FS 110 Stihl FS 90
Edgers: Stihl FC 90&75 Echo BRD 280 Pole Saw: Stihl HT 75 Hedge Trimmer: Stihl HL 45 HS 45