I remember that was the case during the morning peak when they were first introduced, and the reason why the first northbound service started at Peterborough. Later, the power supplies were upgraded.
They could not be used on services to Newcastle for reasons already outlined, so until the rebuilding work at Leeds was completed they were initially restricted to KX-York off peak services.
They were later switched to the Leeds service and gained the name "The White Rose" services.
The 1205 Leeds-KX was one service they worked, and I remember catching this at Grantham on several occasions. As standard class was at the rear of the usual Cl.91 Mk 4 sets, it was a novelty to walk the opposite way right up to the empty south end of platform 1 at Grantham and be assured of the choice of several empty seats in the leading coach, provided you boarded in coach 2 and walked through, as the front and rear coaches were off the platform.
As has been said, they had greater acceleration, and were very comfortable sets to travel in. A pity they are not available for re-hire during the next round of Cl.91 overhauls.