Firstly there is no WCAM 3a...so get you facts right!
Secondly, WR main is mainly plain i.e there are not many gradients as compared to that of CR.
Thirdly, the MPS of section till ET (IGP ET) is 110 kph.
Lastly, RDSO has restricted WCAM2/2p at 110 kph on CR because of the vibrations and wheel slips (on gradients/curves) felt/notified by LPs.