Its not about speed. Its about power and reliability. If WAP-7 can fail anytime so can a WAP-4 or any other loco. In that situation, WAP-7 would be better atleast for the ghat sections of CSTM division and also it's long rake trains like Sevagram, Vidarbha and Punjab Mail, etc. The concentration of 3 Phase was max in NDLS and that of DC and AC-DC locos was only in CSTM+BCT. GZB is the shed for NDLS and KYN is for CSTM. It would be interesting to see whether KYN are given WAP-4 or only WAP-7s like AJNI gets only WAP-7s and no WAP-4s