Brother first of all don't underestimate WAP-4 class loco,it might be old as compared to WAP-5 but it has that optimum speed of 140 kmph which is very much enough for high speed Superfasts trains as most runs on 130 kmph barrier, Now shivganga exp gets WAP-4 basically becoz it was very regular for shivganga in it's initial days just same as sampoorna kranti express which regularly got WAP-4 (now gets WAP-7 Hog) but I do see Shivganga getting WAP-7 Hog loco very soon but not WAP-5