No bro ...

Gurpa-Gunjhadi maximum gradient : 1/80
Limkheda-Rentia maximum gradient : 1/150
Darah hills maximum gradient : 1/100
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Ratlam elevation = 480 m , Vadodara elevation = 32 m

End to end Gradient change = 450 m ...

Dhanbad elevation : 222 m , MGS elevation : 65 m
End to end Gradient change = 157 m


Now compare maximum height / elevation ...

Dara ghats mean height : 600 m approx

Limkheda - Rentia ghat section(Ratlam-godhra) maximum height : 600 m approx

Gunjhadi ghat section maximum height : 370 m


Now compare total length of ghat section :

Kota-BRC = 15 km + 28 km = 43 km

MGS-Gaya = 22 km

Tunnels in BRC-Kota Section is just 1. Number of Curves are less.
Tunnels in Gurpa-Gujhandi region is 3 with 1 tunnel being 1444 mtr long.
Maoist infested, High Freight Route, More curves, more station density.
BRC-Kota 528 kms & 73 station in between @ 7.233 KmpRS Density.
DHN-DDU...
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404.7 kms & 76 kms in between @ 5.325 KmpRS Density.
KmpRS = Kilometer per Railway Station. The unit to calculate Density of railway station in a Major Trunk route & the Distance between 2 Railway Stations in Kilometer.
Major Bridges in Kota-BRC section:- Choti Kali-Singh Bridge at Chaumahla Shipra Bridge at Thuria, Chambal Bridge at Nagda, Mahi Bridge at Bhairogarh, Dhamar River at Dhamarda. Total Length of Bridges is 2.5-3 kms in total. Longest bridge:- Chambal at Nagda 529 mtrs.
Major Bridges in DHN-DDU section:- Barakar at Parsabad, Dhandhar at Paharpur, Phalgu River at Gaya, Dava River at Rafiganj(HWH Rajdhani Accident Bridge), Madad at Jakhim, Adari & Punpun River at Anugraha Narayan Rd., Sone Bridge at Sonnagar-DOS, Kudra River at Kudra, Durgawati River at Durgawati, Karmnasa River at Karmnasa. Total Length of Bridges is 6.325 kms. Longest bridge:- Sone at Sonnagar-DOS 3075 mtrs.
1st of all Station density in MTJ-KOTA is less than GZB-CNB. Hence speed of NDLS-KOTA is more than NDLS-CNB. Average travel time in NDLS-KOTA section is 4 hrs 45 mins. Average travel time in NDLS-CNB section is 5 hrs 15 mins. Fastest train in NDLS-KOTA route:- 12951/52 MMCT Raj; Fastest train NDLS-CNB route:- 22435/36 BSB VB. VB in NDLS-KOTA route will take 3 hrs 45 mins, 25 mins faster than NDLS-CNB route.

So Mumbai-New Delhi Route has less challenge of being the fastest.

Not to mention GZB-DDU route is way more oversaturated than MTJ-Kota route.