Well, it looks like a lot of people are having similar (not the same) question lately, me included
On the end - fate decided for me to go with elmar over summar and summitar
Good thing (for some it is bad) about Leica lenses is that every lens has specific, often unique character - so you can always make good choice, and then when you got more money - another good choice.
So go for the elmar now, and later buy summicron also . And never ever sell Leitz lenses unless you absolutely must - you will end up buying it again and losing money . Life is too short (to safely remove hardware)