it isn't about reaching the temperature, thats another benefit but main purpose of using 0wxx or 5wxx is minimizing the wear n tear occurred achieving that temp and lower viscosity oil provides better protection at that. the 2nd no. corresponds to higher temp.
there isn't any point in arguing, i'm just recommending something better compared to the already good because when someone's asking here he'd want the best option.
it is not like i'm recommending him something unsuitable for our climate like 0w-20 (oil to be preferred by user manual for international market swift). and talking about our climate, what about the oil cooked in jdm cars idling in traffic jams of Tokyo in summer subject to temps as high if not greater? still they are using 0w-20 in most new cars.