There's no reason to think that 'Green Giant' and 'Smaragd' will up and die after the brief spans you have stated for each here.

Ilex x attenuata 'East Palatka' is a nearly spineless American Holly look alike in size and form. Zone 6 may be pushing its range.

Do you live on some sort of estate? Or are you developing an arboretum? If not and just a typical residential property, I would not be overly concerned about tree lifespans. It would be very rare for any tree planting on a typical residential property to still be around 150 years later. Typically when a property changes hands - on average, just shy of 15 years - the new owners redo the landscape according to their taste. They might decide to keep and maintain some sort of specimen tree, usually a large deciduous shade tree but a multi-plant screen or wall of the same kind of evergreens does not necessarily offer the same kind of appeal. Or fit with everyone's opinion on what the garden should look like.

Select whatever you like that fits your other growing requirements and don't worry about "leaving your mark" :-) You won't be around in 150 years and chances are very good that whoever is residing there will have different views on what that "mark" should be.

-Ilex x attenuata 'East Palatka lifespan = only 40 years.

-Green Giant lifespan = again, = unknown, could be great, could be only 50 years.

New homeowners rip out older, established plantings all the time. It is pretty much a constant topic on the Landscape Design forum and I see it routinely with my own client base. People want to put their own spin on their property and their tastes may not match yours. It has nothing to do with "snobbiness" but just different landscaping viewpoints.

Don't worry about longevity....the trees will outlive you. Just plant what you like.

btw, anything fast growing in the conifer world will not stop growing at some arbitrary predetermined point. 'Fast growing' and your 30' height limit are not compatible.

“New homeowners rip out older, established plantings all the time.”

Yes, that confirms my experience — both as a buyer and seller.

nah, there are plenty of conifers/evergreens that don't max out over 50ft.

I just figured I'd ask here rather then search each type and then about their windthrow resistance, soil type acceptance, growth rate, mature height, lifespan, disease resistance, etc.

Don't worry about longevity....the trees will outlive you. Just plant what you like.

It's not for what I like, 'leave my mark' just meant a good, solid tree in the right location that'll last and likely not wanted to be replaced...

..Usually people rip out species that were malpruned or skipped too many prunings and became scraggly.

I probably will plant at least a couple GGiants, it's a great tree except for unknown lifespan..

There's no reason to think that 'Green Giant' and 'Smaragd' will up and die after the brief spans you have stated for each here.

True, 25 years (I meant 25 which a quick googling says, not 20yr), 25 seems underestimated for emerald green arborvitae... Maybe 35-40?

I also meant Japanese Arborvitae, not Chinese. AKA Thuja standishii which is what makes up half of the green giant, I'll search more for standishii lifespan to maybe ensure a bit more that the Green Giant arborvitae might actually live very long. Either way, based on the other half of the GGiant being a western red cedar AKA Thuja standishii that is known to live up to ~1,400 years, I have hope GGiants do last long, but I doubt it's all a simple as just an average of the parent plants, even if disregarding things like growing site conditions.

The trees that are fast growing typically either aren’t long-lived or get large. Yes there are plenty of evergreens that stay under 30’, but they mostly aren’t considered fast growing which is what you stated that you want.

^I'll take recommendations even if they're not fast-growing.

I'm surprised to learn that a lot of trees and shrubs don't live nearly as long as I expected... but I think there should be some that fit this criteria

Some people die in childhood. Others can live past 100. The life span of a particular plant specie you are finding online can only be guesstimated averages. There are no guarantees. This focus on longevity is rather absurd. If you want to leave your mark for 150 years, do it in stone.