I think it sensible of NX to opt for E400 double deckers as the Volvo B5 and Wright Streetdeck only have 5 litre, 4 cylinder engines and going too small with the engine has not generally been successful. The Leyland Tiger Cub, Bristol, with the Gardner 4LK and more recently the Volvo B6 were not popular. Reading these columns some drivers prefer the Trident to the E400 as it has the bigger Cummins engine.