Unless colourcoats has significantly changed their formulation of 5N since I used it some years ago, it should be noticeably blue. Having said that, I understand the urge to seek a bit more saturation of colour for the sake of your model looking better and/or more like you imagine it.
My personal choice for 5N, that I've now used for quite a few projects is Humbrol 104. Dark Sea Blue type colours intended for late war USN aircraft (e.g. the Testors you mention) should also be "good enough". Actually I use H104 for those aircraft as well, and for 20-B deck blue, and the CV flight deck stain depending on period. It's a great colour...
Also remember that the final perception of the colour depends on finish and weathering. Late war US carrier aircraft are gloss so the sea blue looks darker and deeper. A grey dry-brush on a ship will take the edge off the blue a little and make the overall effect a bit duller, but a satin coat could enhance the colour and give it a deep freshly painted look. Some ships in Ms.21 look almost black in B&W pictures, while others, clearly faded from long service, are more subdued.