It's just a pity so much of the network had/has TSRs that mean hardly has a train accelerated to 100 it is braking again for the next restriction. Nowhere on the network has a line speed over 100.
I honestly think the amount of money the 201 shape saved in fuel economy could be counted on one hand but that's a gut feeling and I absolutely stand to be corrected!
Perhaps the intention was there however. Unfortunately Irish Rail made a number of senseless decisions along the way, the needless scrapping of the mkIIIs a few years after buying all those locos being the most obvious.
Still plenty of push pull and loco hauled trains here in Germany, despite the advent of the multiple unit.