Mumbai Chennai trains take 9.5-10 hours to cover Mumbai to Guntakal. Mumbai Bangalore trains take 11.15 hours. Straight 1-1/2 hours extra.
Guntakal to Bangalore, you can save cool 4 hours. So 5-1/2 hours can be saved. Atleast 5 hours.
What is the point of doubling electrification etc if journey time is not reduced?