Hi Rob,
Man, you are full of surprises! Now where on earth does the 'other' kurassier metalhelme appears from, eh??
Suddenly you have 2 now. Pls dont tell me that you have it for a bargain price AGAIN
1st things 1st tho,
Thank you so much for the detailed pics, they are lovely!
I am not an expert on these but i will try my best to answer depending on my observation.
I am convinced that what you have is an officer GdC, the "trefoil brasses " that you mentioned is actually a pair of officer rossetes, an EM only uses a M91 type sidepost. Like your 'other' kurassier metalhelme, darn, the term 'other' gets on my nerve...

LoL
And the pair of Prussian and Reich kokarden are officer's, i dont really understand why there are 2 holes on each 4 sets of holes for the spike base....One reason could be that, well, there are known cases of 'cheaper' private purchase helmets, including pickelhaubes, some officers are not so well to do, hence they will opted for a used helmet as they were cheaper, hence the extra holes etc but still belonging to the same regiment as the extra holes correspond with the presumed 'original' holes.
The Garde wappen is DEFINATELY private purchase, the details are very pronounced, whereas the EM is not so defined.
Pls note the reinforced 'rear spine' directly behind the 4 sets of holes for the spike base, those rear spine only exists on officer's helmet and the step visor is also the distinctive mark for officer's kurassier metalhelme.
But once again, these are my observation, I could be wrong.
Here is Ken's site, he has an EM GdC with parade eagle metalhelme, its a good example for comparison on why I am very convinced that yours is officer's. Compare the his visor, the rossettes, the non existent rear spine, garde wappen, liner etc with yours.
Judging from the color, the spike base, the welding etc, your parade eagle is EM, and like you said, it came with the package.....ooooh, I am sooooo jealous!

A parade eagle alone will cost more than the 140 Pound.....
http://www.derrittmeister.com/04395.htmAs for your 'Other' metalhelme, thats something very new for me, its an eye opener, why does it has a shorter lobster tail rear neck guard? Why does it has a dragoon/Jaeger zu Pfferde prussian eagle wappen? is it an older kurassier like the 1862 version?
I need to browse thro the books again and will get back to you asap, this is so exciting.
By the way, I will keep my eyes open to find an officer fluted spike for you, even if I dont have aGdC, but i will be very happy and proud if my friend has it.
So sorry for the long reply. You have an amazing collection of kurassier metalhelme that I could only dream of.
Hope this helps,
Mush