I know everyone is all over the 45/1.8 but there is a lot to be said for the Leica 45/2.8. I appreciate the aperture is slower but this is the one lens I cannot bear to part with. In my calculations to sell bits of kit here and there I always come back to feeling I can't part with this lens. Incidentally, I'd sell all my Leica kit first, that is how good I think it is.
Just my two cents.
I don't know the 45 f1.8, so I can't compare, but I'm right with you on the Leica - the nicest macro lens I've ever used I think.
I'm interested to see how good the macro mode on the 12-50 is (that's 45mm as well).
all the best