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.
2013 E92 M3 | Mineral White Metallic/Black/Carbon Leather | M-DCT | ZCP | Premium | EPS | Sirius | Michelin PSS 255/275 | 3M Tint 35% Sides & 20% Rear | IND Light Smoked Reflectors | LUX H8 5000K | OEM Black Chrome Grilles & Gills
Past BMWs: 2012 F10 535i, 2011 E90 335i, 2009 E90 M3, 2008 E70 X5, 2006 E90 330i, 2004 E46 330i