I don't know if this qualifies as high end, but in the three or so years of engaging in this activity, I've spent most of my money on providers in the $500 - $700 range, with several forays into the $1000 plus category.
My general impressions?: the $1000+ women have not been worth it for me, either in the looks or service/demeanor/fantasy-fulfillment department. This is not to say that they cannot be worth it for anyone, and I've had at least one occasion with a $1000+ provider that was pretty damn awesome. But the main reason I say this is that many of these ultra-expensive girls slum at the mid-high-end agencies for the volume of calls. The same girl sometimes will book out at wildly varying rates at the same agency, based on whose "picture" you ask for, and what the agency thinks they can get out of you. I've had several "high-end" providers tell me this. Think about it: how many sheiks, internet millionaires, and Wall-Streeters (who haven't lost their shirts yet in stocks) are out there and who are willing to blow a grand, two grand or more for an hour with one of these girls? So for me, the mid-high-end girls have come closest to fulfilling the kind of experience I look for with a provider, at a price that at least hovers around being reasonable.
On to my specific impressions of agencies. Now, I don't claim that anything I'm about to say is definitive, as my experience with some of these agencies is limited. And as always, the experience depends ultimately on your tastes, your mood, and whatever chemistry you're able to achieve with a particular girl on a particular occasion. Also, I'm not as concerned with what acronyms a girl is willing to perform, but rather with her overall demeanor, warmth, and personability -- in short, how she makes me feel to be with her. With these caveats in mind, in no particular order:
EliteModels.net (same owner, I believe, as Chez Brigitte; at least according to the caller id on my phone): the times I've used them, photo was definitely fake. Phone girl will insist that all photos are real. Service and attitude vary somewhat: some girls DFK (which is something I particularly like), BBBJ; others won't consider it. Looks, while good, have honestly been less than what I was expecting. Too hit-and-miss imo at this price ($800 - $1200 for the girls I tried)
Enchantee (I think they're called Portfolio Elite now): the one time I tried them, it was an egregious bait and switch. The girl didn't come close to being the one in the photo, either in age or looks. She was plenty nice and accomodating, but not worth the fee imo in terms of looks.
Fleur de Elite: pics are real, at least the times I've used them. Couple of very nice experiences, although unfortunately both with girls no longer with them. Other times, service was quite mechanical, uninspired and rushed. Looks generally are of quite a high caliber at this agency. But given the varying service, too hit-and-miss imo at this price ($1000 - $1500 for the girls I tried).
Charles' Angels: pics are real, at least for some of the girls; some of the girls I've seen had no pics. The looks and service here in my experience vary wildly. Some girls are extremely accomodating (one offered me bbfs, which I declined of course); some are pretty cold fish and not worth the fee imo in terms of looks.
Belladonna/Lefleurissimo: laughingly fake photos. Looks and service though, the couple of times I've tried them, was surprisingly good at the price ($500).
Mona Lisa models: looks vary wildly, but service and attitude have been pretty consistent. Some photos on site are real, many are obviously fake.
I realize after going over this list that I haven't yet found an agency yet that I'm fully happy with; sorry but I guess my post doesn't really respond to the original poster's query. I guess if I had to pick one agency that I was happiest, or least unhappy with, all things considered, it would be Mona Lisa. There are others I want to try, but haven't gotten around to: American Beauties, Tower Models, NY Elites. But I hope my experiences help you guys as you wade through the sea of agencies out there. A couple of other points: some agencies will email real photos of girls they think you might like after you've used them a few times. And some girls will offer you their phone number so you can see them while cutting out the agency middle man. I'm not sure of the ethicality of cutting out the agency that introduced you to the girl, but I personally don't lose too much sleep over this because I know there's a pretty good chance I'll use the agency again. Hope some of this is helpful, and good luck.