YES! And not only that, it is going to shift better with 4mm housing than with 5 if you are using a 1.1 or 1.2mm cable. Anyone who thinks housing isn't important hasn't worked on many modern drivetrains. Maybe you can get your syncro working fine with brake housing but it is going to work better with proper shift housing.

Re: the sub topic that has started about indeed shifting... someone in another thread was saying how campy got it right with ergo from the get go... and I was thinking.. "really!? you think so". Even in the early 2000s ergos shift performance was STILL inferior to the light action and precision of shimano.