What is the best hosting provider for an enterprise scale Rails application?

We have just finished the early stages of testing our application and
are looking to roll it out to our customers in the coming weeks
(approx 12000 of them), our application manages financial transactions
and has a huge amount of liability involved, therefor we can’t afford
it to f-ck up, our development team has spent a lot of time making it
as bullet proof as possible, including building a asynchronous real-
time backup of all transactions to a second rails app and mysql
database run on a second server.

Also all of our customers are located in Australia and so far we
haven’t found any experienced hosting companies willing to provide
guaranteed support if the sh!t hits the fan, so we are looking to host
in the US with minimum latency as possible.

Has anyone had similar experience, or know of a hosting provider that
is by bar better than any other for this type of application?

I haven’t used them personally, but Engine Y. focuses on this sort of
hosting. They’re not cheap. They’re enterprise-oriented.