3x10x40-50mm will be just fine. FOV will be slightly larger with the bigger objective but it won't make a huge difference. It really is personal preference and wouldn't try to steer you either way, in equal quality scopes.

However if you buy a bigger objective scope in lieu of a better 40mm (optically) then it becomes a diminishing return. Also if you use a 50mm with higher rings and it pulls your cheek of the comb of the stock then I would advise you to stick with a 40-42mm to mount it for proper shooting position and fit.