I have traveled only in a non-AC DD (Sinhagad in 1995) and never in an AC DD in India. Anything more than 5 hours does seem painful. However, the BCT-ADI DD seems quite popular and is running full. Is that true?
Also, that DD goes consistently at 120 kmph. If so, why is the KR DD restricted to 80 kmph when the JS/Rajdhani/Duronto do 120 kmph? Tunnel clearance issues?