Viscosity is one thing and API grade like SG, SJ, SN, SM etc is another.
By the way, temperature of twin cities exceed 40 degree centigrade in summer, so even by your formula mentioned above, 10-40 suits more.
I would recommend the OP to go for SGO Premium (10w40 API SG)
The interval recommended by Suzuki is 5000 Kms although I change it at 3500 Kms because in summer my car idles with A/C ON. And in such case Kms are not increasing on the odometer but engine is still working.