I have seen situations where the HD glass gives better resoluation in low light conditions... but it is minimal. The real factor is to take advantage of the Leica Rebate like Flyingbrass mentioned... that is a super deal! Either way, you won't be sorry! NJS
I've got the non HD model and I love them. Great glass. If I had to do it all over, I'd get the exact same pair. I don't think the extra money is worth the small percentage of gain, but that's me. If money is no object, go for the HDs.