नहीं कोई गम, रेलवे से हैं हम - Aman

Yes, there is no difference in speed/acceleration/load capacity. The Microprocessor control, SIV and VCD are all for improving reliability, safety and making fault handling easier. They have got nothing to do with the performance and speed of the loco.
All WAP4s have the same specifications when it comes to traction, and all of them rely purely on the skill of the Loco pilot for their performance.
Microprocessor WAP4's are not really next-gen. A lot of WAP4's from all sheds have...
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been retrofitted with SIVs, Microprocessor control and VCD over the years. Its just an efficiency upgrade, not a performance one.

Well, you don't have to accept my 'belief'. You can refer to RDSO/CAMTECH's manual for Microprocessor controlled electric locomotives - click here
This is the official manual published by RDSO and CAMTECH regarding the microprocessor based electric locomotives. It is very clearly mentioned throughout the manual that this is just for better reliability and fault management. The new systems are only a part of the control system, not the traction power system, which decides the power output of the locomotive.
WAP4's are tap changer locomotives....
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The technology used in them is obsolete and development on it stopped in the 90's itself (In other countries, the technology became obsolete in the 80s only) and also other than minor changes, no improvements are possible in the design without making major redesigns, which would have been a waste of time and resources with 3 phase locos already available.
They were simply produced till 2015, because IR struggled to solve the issues they were facing with 3 phase locos. And even though the traction technology in WAP4 is obsolete, they were proven, reliable designs, so CLW continued producing them until the 3 phase locos matured, and along the way, added some features to improve the reliability and fault management more.