What speed difference? 9mph? Hardly a gaping chasm of difference.... Coupled with the Chinook's ability to work at higher altitudes, it's far superior reliability and it's vastly better lift capacity, it starts to look quite promising for the chinook.
The Merlin saga is typical of UK government procurement processes. Every Tom, Dick and Harry has had their say on what they'd like the vehicle to do in their own little fantasy world, which the gov't/MoD tries to get the supplier to fullfil on (Who proptly rub hands and say "oooooh that'll cost you") and we end up with an aircraft that is hideously expensive, massively behind schedule and a jack of all trades and a master of none.
Apart from it's fancy engine management systems it's hard to see what the merlin can do that it's more capable and less expensive competitors can do.