I would be happy to fly on an older aircraft as long as I know the maintenance schedule has been good.
Just checked LGW/YVR/LGW against BA in June and fare in the premium cabin is some £800 cheaper than BA WTP with same seat pitch.
That is quite a difference. We do this route frequently, always in the past with BA next time booked with AC but Westjet looks like a future favourite with that much price advantage.