Best way to sync ONLY SOME photos to iPhone from Aperture?

Hello,

Still using Aperture 3.6 with OS X El Capitan here, and willing to use it some time more...

My situation is this: I have an Aperture Library of nearly 20 Gb of images. As you would suppose, I'm beginning to run out of HD space.

And I have another issue: there are a LOT of images that are not worth keeping synced across all my devices.

I want to choose some of them, only those I think are worth keeping in sync, but I'm wondering what is the best way to do it, reducing the work to do.

So my question is: what is the best way to sync only some photos, and keep the others from syncing to other devices AND iCloud's Photo Library?

My photos are spanning across their projects(events) and I want to keep them organized as they are.

I have them rated to identify the best ones: unrated will mean they will not be synced.

First, I have thought to move the photos to be referenced, as I've read that referenced images will not be synced.

Do you think that could be a good solution in a future workflow?

For all the RAW originals, I mean to do the same, so only their JPGs versions will be synced. Moving them to referenced could also solve my issue?

I've thought in smart albums, but don't know right know how to use them to reach my goals: not sync but keep organized the synced ones.

Any help would be appreciated.