I've often thought the Buxton/Hazel Grove diagrams would be ideal for them. They're based in the Manchester area and run a lot of distance under the wires (a slim majority of their overall mileage, I believe, now that Buxtons and Hazel Grove terminators inter-work). They also don't go through Castlefield and have a very long layover at the Buxton end, which hopefully reduces the chance that a technical issue completely destroys the service. And they're currently 4-car 150s, so a 769 would be a like-for-like replacement with most passengers not even noticing the difference.