I'm also a 34B and I've tried a lot of different brands. My personal favourites are the Moving Comfort bras, specifically the Phoebe model - I've got two of those and have run a marathon in each with only one small patch of chafing at the centre back (which was absolutely fine on my 20 milers go figure).
I'm more annoyed about the fact that there's no bag check. For a race where you get covered in paint, it's a bit rich you can't bring a change of clothes. The organisers suggest you carry the provided poncho with you as you run so that you don't get paint on public transport on the way home.
Oh, and there's no medal, either.
This race had better freaking be as happy as advertised, or I'm going to be seriously pissed off at what a rip-off it is.