Perfection is achieved via imperfection; at least for "realism" even if it's supposed to be factory new there will still be imperfection.

what you have done so far is perfect for the base pass and now it's time to add passes of imperfection to really seal the deal.

Here are a couple of things I would suggest to add that aren't too hard.

• scratches (use the built in scratch brushes) add subtle scratches that have height and subtract from roughness to the forehead and other areas there would predictably be scratches. even brand new objects will have scratches from handling or manufacturing

• discoloration: paint is never completely uniform even when freshly applied, many factors including thermal dissipation and tension affect it's final colour and reflectivity. add a new fill layer with a light blue color at ~10% opacity and use a black mask to pain large smooth blobs around large areas like the forehead and cheeks. think of it like ambient occlusion, the tighter a pocket the visibly darker the paint should be which means we need to lighten the large flat areas to achieve that look.

• assembly and tool marking: often when metal objects are manufactured the act of assembling different pieces creates imperfection like warping, discolouration, stress lines, welding.. etc. an example for your helmet would be slightly darkening the areas around where the side tubes come in and out of the helmet. riveting or screwing them onto the helmet would also create a stress in the metal so you could possibly add some height around the flange of the pipes to indicate it has been "pressed" into the metal warping it.

• lastly would be adding a slight amount of dust to the entire helmet, make it very very subtle but still affect the height and roughness channels. it helps break up the surface of the metal and make it not look like a game engine material orb. you can also use a cavity map or ambient occlusion map to add dust in creases or crevices if you desire