One of the blues would have been my top choice as well (I ended up getting AW again because I wanted to find an '09 for the financing). I love them both and I don't think you can go wrong with either because they are very similar, as you said. The Le Mans is a little bit lighter/brighter and less purplish.
If it were my decision, I too would be torn but would probably go with Le Mans because to me it looks like more of a pure blue, and it also seems to be a bit less common than IB for some reason.
2015 ///M3 | BSM/Full Black/CF | DCT | Silver 19s | Executive | Lighting | DAP | Adaptive Suspension | HK | Enhanced USB | Tint
Past BMWs: 2014 550i, 2013 M3 ZCP, 2012 535i, 2011 E90 335i, 2009 E90 M3, 2008 X5, 2006 330i, 2004 330i