Whilst I may not be quite as forthright as others are, there is a lot of truth in what they are saying.
If you go strait to the £350ph girls, they may not, in fact quite often ARE not as good as their price suggests. That said, I hear only great things about Rio Lee, so if you are going to go that way, I'd go for her. I've heard it from respected punters and other escorts alike.
But...
I think to get you going you'd do well to look for some if the well quoted and somewhat cheaper superstars. Platinum Cindy is universally acknowledged on here as a star performer and vs price she is right up there. The problem you have is that she only sees guys with adultwork feedback.
So if I were you, I'd make your first punt with a well quoted and consistent girl in the considerably cheaper £150-£200 per hour category and work toward Cindy for a great experience.
If you still feel the need, you can always punt upwards, but if you get a girl at £350ph who believes her own hype, is a but delusional about her worth and doesn't give the service you might expect, you may think that it is entirely normal because you have nothing to compare it to.
I'm thinking someone like Hot Ameera might be perfect for you. She's on Adultwork.
Good luck!
