Cointreau It's not really my second choice, I'm just savouring it all, and enjoying thinking she would almost certainly get in. I think it's gonna be too much hassle to get to and too pressured. But I'm figuring, seeing as I've waited 6 months for this, since she sat for Nonsuch, I'm going to take my time - tee hee - and muse over a 
With regards to Nonsuch and Wallington, Nonsuch is harder to get into, because the tests are harder. The general consensus of the DC at the school-gate was that it was very, very hard. The Wallington test, by comparison was easy. (It's still bloody hard!)
If your DD is good at Maths, you are half-way there at Wallington.
If your DD is a 'reader' she'll probably be OK with the verbal reasoning.
IME DC find the non-verbal reasoning the hardest.
Having said all that, more girls pass the Wallington test and there are still only 180 places, so from that point of view it's hard to get into IYSWIM. Lots more pass, but they can't all get in. Even though they don't all get into Nonsuch, not as many pass.
I have a few books which explain how to do it, and get harder and harder - until they're nigh on impossible! If you want to PM me your address I'll post them to you, though I completely understand if you wouldn't want to!