I think all the Trilogy are just a tad too big for a 6.5" wrist personally as one-and-done watch, because of the lug-to-lug and the size of the bracelet mainly - without the bracelet looks fine. Also looks fine with the bracelet if you wear your watches higher up on the wrist and are otherwise well built. Something more the size of the Speedmaster Reduced (10-11 mm thickness, 38 mm, and 44 mm lug-to-lug) sits better and looks more elegant on a slender wrist I think, but there is no adjusting the size of the Trilogy to fit this design into a smaller form factor. This is as small as it gets, and it's still small by modern standards.
To give you an idea, I have a 6.6" wrist and can 'feel' my Speedmaster Trilogy on the wrist all day - due to the size of the bracelet, clasp and the weight of the watch. With the Reduced, I can wear it all day, even go to bed with the damn thing and I will never feel it, it is like a part of my arm - as it should be for a one-and-done. Nonetheless, I love the Trilogy Speedmaster but I have to concede that the Reduced is just a better form factor for all day wear - the best watches are the ones that you forget are there IMO.
I would buy from a seller with a good returns policy, or buy at a price whether you will lose hardly anything if you resell (there are several offers in the $4300-4500 range these days). Buying a watch unseen often leads one to reconsider later and a journey of flipping in my experience.