I usually get a stable 450 - 550 ms. IT usually gets better later at night. Going has low has 350ms.
With that said I have to say that sometimes there are some disconnections from the network, but that happens to all our connections in south Africa. They are pain in the ass but they don't happen that often.
The connection even handles a stable 450 - 550 ms in Alterac Valley (PVP battleground of 40vs40). It is a really awesome connection, but it is costly!
I suggest trying with a prepaid card to see if it works well for you has it did for me.
I go through around 3gigs a month, that is because I do a lot of PVP.
Take care & good luck ;)