Hi BlueOPawprint and welcome!
To start with your last question first: Pearl Paradise has several very nice pendant findings, if You are not able to finish it with a pearl, they gladly will do it if you just choose a pearl You would like. I stated wrongly that they have enhancers, that?s not true, they have pendant findings only, sorry!
Secondly you could always try a local jewelry shop for enhancers.
Thirdly: Yes you can use that enhancer you have on your Mikis, they wont suffer if you use it just occasionally. But be sure to check the overal condition of the silk on this strand. If it is old, it could be that you need to restring it first for safety reasons. And no, why should your 2-stone diamond pendant look lost on an enhancer?
Of course, 6-6,5 mm pearls are not very large but only if the combination enhancer and pendant is too large, it might be a bit too much for the strand in weight terms and looks.
Now to the more important things:
First you need to be quite clear about what it is that YOU WANT and not what other people migt think is suitable for you. It is you paying an not they, so forget them!
Tahitian pearls are lovely and if you have 1,600 dollars to spend, the strand from The Pearl Outlet looks superb! And 10 mm is a substantial size but not too large either!
But for that kind of money you could email or call Paerl Paradise as well, because they could put together a strand just for you, according to your wishes. They have lots and lots of pearls to choose from.
The one strand that Hanaleimon sent back is circled but as You write that you are not so interested in circled ones, perhaps you should go for the drops, like Terry?s.
The American Pearl shows a strand that looks perfect in shape and luster but for 1,000 dollars you would not get that kind of Tahitian strand with round pearls! As Pearl_dreams pointed out, this is a company you should perhaps be cautious about. Read the posts (there are several).
If you have a strand with size 9-10 mm, an enhancer will look good.
Still, if You should choose the strand from The Pearl Outlet I think you would be very pleased.
However, don?t forget to take a very close look at all the nice Freshwater strands, they are lasting a lifetime and have very attractive prices compared to South Sea pearls.
A last word of warning buying form China or Asia: You never know what you?ll get, shipping costs are usually exhorbitant and their return policies might not make you happy! Stealing photos from other companies is a method that is used widely too, expecially if you gor for Ebay, so.....
Good luck and let us know once you have decided...