The average speeds of both BPL shatabdi and Sealdah - NDLS duronto are almost the same. In fact second spot in terms of avg speed is occupied by the latter. Max speed of a train in INDIA is that of BPL shatabdi in the AGRA - Mathura section.
Infact, the NDLS - SDAH duronto is twice as long as BPL shatbdi. And the average speeds of the BPL shatabdi n duronto are almost the same as i stated earlier